When he stepped onto the Royal Opera House stage to accept his first Best Actor Bafta on Sunday, Leonardo DiCaprio was cheered on by some of the most famous actors in the world.

But as the 41-year-old Hollywood star launched into his acceptance speech, there was only one person in the audience who caught his eye.

Having thanked his co-stars, DiCaprio’s gaze settled on a smiling 73-year-old woman with ash blonde hair and feline eyes that mirror his own.

‘Lastly, there’s one person I have to thank,’ he said. ‘I would not be standing up here if it wasn’t for this person. I didn’t grow up in a life of privilege. I grew up in a very rough neighbourhood in east Los Angeles.

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Leonardo DiCaprio is joined on the red carpet by his mother Irmelin DiCaprio at the Academy Awards in 2014

‘This woman drove me three hours a day to a different school to show me a different opportunity. It’s her birthday today. Mom, happy birthday. I love you very much.’

On the face of it, DiCaprio’s dedication might be dismissed as nothing more than a momentary display of filial affection. But a quick glance at his career serves as a timely reminder that his mother Irmelin has been by her son’s side ever since he shot to fame in the early Nineties. It was Irmelin, dressed in a black velvet coat dress and matching choker, who escorted a teenage DiCaprio to the 1993 premiere of What’s Eating Gilbert Grape.

She was there, too, at his side for the premieres of Romeo + Juliet in 1996 and, along with his beloved Russian grandmother Helene, Titanic in 1997.

She has sat at his table at countless Oscar and Golden Globe ceremonies and watched him from the wings on numerous film sets.

She has even been given various cameo roles in some of DiCaprio’s films, for example, playing a nun in the 1995 film Total Eclipse. Even this week in London, where DiCaprio spent several days after his Bafta win, he was spotted taking his mother to exhibitions at the British Museum and the Science Museum, where the pair saw the Mechanics Of Genius exhibition dedicated to the actor’s namesake, Leonardo da Vinci.

If there’s any doubt about just how much DiCaprio adores his mother, it’s worth remembering that he once claimed that when he needed to summon up feelings of grief for an acting role he simply imagined her ‘horribly charred in a fire’.

Or that when he outbid Paris Hilton for an £8,000 Chanel handbag at a charity auction in Cannes last year, it was because he wanted to buy it for his mother.

Indeed, while DiCaprio is notorious for his predilection for young, blonde models and has squired an endless bevy of beauties, among them models Gisele Bundchen, Bar Refaeli and Erin Heatherton, actress Blake Lively and singer Rihanna, it seems that Irmelin is the only woman to have endured in his affections.

DiCaprio biographer Lisa Arcella told the Mail this week: ‘Leo often takes his mother as his date to awards shows. She loves all the glamour and excitement, and he loves to spoil her.

‘He wants to repay her for all the sacrifices she made when he was growing up. But it runs deeper than that. They are extremely close.’

Some observers in the U.S. have even speculated that Irmelin is the real reason behind DiCaprio’s failure to settle down and find a wife.

See Leonardo DiCaprio updates on his relationship with his formidable mum

Leo shoots scenes from Wolf of Wall Street. Ladies man Leo was joined by a group of bikini-clad women for the movie re-shoots filmed on a yacht in Los Angeles

Certainly, a closer examination of DiCaprio’s childhood sheds light on his emotional declaration on Sunday night that he simply couldn’t have made it without her — and goes some way to explaining why none of the women in his life have matched up to her.

But if DiCaprio likes to remind his fans of his journey from the mean streets of East Hollywood to the top of the Tinseltown ladder, his mother’s own extraordinary story could have come straight out of one her son’s films.

The daughter of a Russian refugee, Helene Smirnoff, and a German coalminer, Wilhelm Indenbirken, Irmelin was born in a German air raid shelter in 1943.

She spent the first two years of her life in hospital near the family’s home in Rhine-Westphalia, first with a broken leg and then contracting infection after infection and suffering from malnutrition so chronic that her stomach was distended.

DiCaprio has retold this family drama in several interviews: ‘When you see a picture of my mother, it’s heart-breaking. It brings tears to my eyes, knowing what she’s been through in her life.

‘I have a picture of her — her first photograph, with this tiny little skirt — and she’s emaciated. She had a belly full of worms.’

The Indenbirken family, including 11-year-old Irmelin, emigrated to the U.S. in August 1955.

Poignant immigration documents seen by the Mail this week suggest the hardships the family must have suffered when they arrived in New York from Hamburg.

Actor Leonardo DiCaprio has dated a series of woman, including Israeli model Bar Refaeli, who he is seen sitting courtside with as they attend the NBA basketball game at the Staples center in Los Angeles in 2010

The manifest of the ship, M. V. Italia, describes the family as ‘aliens’. Their first home was a humble apartment in the Bronx.

It was in 1963 while studying to be a legal secretary at City College in New York that Irmelin met George DiCaprio, a long-haired beatnik who hung around with the likes of poet Allen Ginsberg and members of rock band The Velvet Underground.

The couple married several years later and moved to Los Angeles at a time when California was seen as the land of opportunity and sunshine.

The reality was rather less rosy. While distributing comics and alternative literature in his spare time, George, the grandson of a Neapolitan immigrant street cleaner turned real estate broker, worked as an installer of asbestos and fireproof roofing, while Irmelin did, indeed, become a legal secretary.

Yet neither were paid well and they could only afford to rent in one of Hollywood’s poorest districts.

By the time Irmelin was pregnant in 1974, the couple were drifting apart, but they embarked on one last adventure together before the birth of their only child — a trip to Florence.

It was there in the Uffizi Gallery that Irmelin stopped to admire a painting by Leonardo da Vinci and, after feeling her baby kicking inside her, settled on a name for him.

Back in Hollywood, Irmelin and George separated, but decided to rent adjacent bungalows with a shared garden so they could raise their son together.

DiCaprio, who spent his summer holidays with his grandparents in Germany after they returned there in 1983, seems to have been left unfazed by his parents’ unusual arrangement, claiming in one magazine interview that it ‘never bothered me’.

He added: ‘As far as my family is concerned, my parents were the rebellious ones — they’re people who have done everything and have nothing to prove.’

Leo poses with the Bafta award for a leading actor for his work on the film ‘The Revenant’

But it was an undoubtedly unconventional set-up, with DiCaprio dividing his time between his mother and father; his father’s new wife, an actress called Peggy; and an older stepbrother, Adam, an aspiring actor whose early forays into TV were to spur on DiCaprio.

Those early years, growing up in East Hollywood, read like a rags-to-riches story.

There, in an area he nicknamed ‘Scumsville’, the young DiCaprio was surrounded by prostitution and drug-dealing.

Neighbouring properties included Le Sex Shoppe and The Waterbed Hotel, and as a toddler he claims to have witnessed gay men having 𝑠e𝑥 in broad daylight and junkies smoking crack in an alley close to his home.

But if Irmelin’s vision of Holly-wood as a glamorous town of golden opportunities had been swiftly dashed, she was determined to give her only son the best possible education.

First, she successfully applied for a scholarship for her son at Seeds Elementary School, a private Montessori-style establishment on the university campus of UCLA.

From there, DiCaprio won a coveted place at the Los Angeles Center for Enriched Studies, which boasts one of the best academic records in California and attracts pupils from aspirational families all over the city.

It was this school to which he referred at the Baftas on Sunday night when he spoke of the gruelling three hours his mother spent in the car to get him there and back each day.

‘I got to see how the other half lived,’ he said in a recent interview with Variety magazine.

‘I could see the other world was out there. And if I could get my shot, I would never waste the opportunity. That mentality and that gratitude are still with me.’

He had his first taste of the limelight at the age of just five after auditioning for an educational children’s programme called Romper Room, though Irmelin was asked to take him home because he was too disruptive.

But it was watching his stepbrother earn $50,000 for a series of 20 cornflake adverts that finally spurred DiCaprio to try his hand at acting.

And, once again, it was Irmelin who ferried him to and from auditions. ‘His mother drove him to and from school every day and was with him at auditions in the afternoon on top of juggling her secretarial jobs,’ says biographer Lisa Arcella.

‘Everything revolved around Leo’s needs.’

One of his first acting jobs was a TV commercial for Matchbox cars when he was 15. Within a year, he had won roles on shows such as Roseanne and The New Lassie.

His big break came when, at the age of 18, he was handpicked by Robert De Niro for the starring role in his 1993 film, This Boy’s Life.

When he stepped onto the Royal Opera House stage to accept his first Best Actor Bafta for The Revenant on Sunday, Leonardo DiCaprio only had eyes for his dear old mother

Just a year later, he won his first Oscar nomination playing Johnny Depp’s autistic brother in What’s Eating Gilbert Grape, and suddenly the movie offers were coming in thick and fast, along with the attentions of an array of beauties.

Some of them appear to have been serious, though there has long been speculation that any woman wanting to get close to DiCaprio must first get past his mother.

Actress Blake Lively is said to have fallen foul of her in 2011 when DiCaprio jetted to Italy with his mother to end their relationship.

At the time, a friend claimed: ‘She tried hard to impress Leo’s mum when they met, but Irmelin couldn’t stand her. She told Leo that Blake was far too up herself for him. Leo listens to his mum and the fact she didn’t like Blake put him off.’

Pop star Rihanna is another girlfriend said to have failed to make the grade, while the Israeli model Bar Refaeli, who dated DiCaprio on and off between 2005 and 2011, is thought to have been one of her favourites.

And so despite a career spanning nearly a quarter of a century, not to mention five Oscar nominations, three Golden Globes and this year’s Bafta, DiCaprio has yet to find a lasting leading lady. In the U.S., there is much debate about the reasons why.

Relationship guru and author Dr Gilda Carle claims the actor is simply dating the wrong kind of women. ‘His mother clearly dotes on him and has been wonderful to him,’ she says. ‘Yet he ends up dating supermodels who are into their own looks, charms and personality. He’s a mother’s boy and no other woman can compete with that.’

For now, DiCaprio appears to be resolutely single, despite claims he hooked up with two blondes following his Bafta win: 30-year-old Irish TV presenter Laura Whitmore and 24-year-old lingerie model Roxy Horner.

But don’t expect to see either of them at the Oscars ceremony in Hollywood next weekend.

If, as is widely predicted, DiCaprio finally picks up an Oscar for his role as fur trapper Hugh Glass in The Revenant, it goes without saying that once again it will be Irmelin who catches his eye when he steps up to receive it.