The world No 1 admits to wishing she had a more athletic figure when she was younger but soon learned to love her body.

Posing in a swimsuit for the May issue of Fitness magazine, Williams said: ‘When I was young I thought I should be built more like an athlete – long and lean – not with a womanly figure.’

However, as she found increased success Sernea developed a huge following.

She explained: ‘But then people my age started coming up to me and saying, “I love you because of the way you look.” That was really motivating.

‘So I learned to be proud of my curves and embrace my large boobs. It’s all about loving who you are and realizing that you’re beautiful.’

While Williams is thought of as one of the greatest players in history, she also enjoys sport for fun.

‘For me it’s so important to mix it up, I ran, and then I biked,’ she tells Fitness. ‘Then I did elliptical … I tried yoga.

‘I started dancing because I couldn’t train when I was sick. We started making up moves, and it was fun. Now I run for 10 minutes and then I dance.’

Proud: Williams has learnt to be proud of her body after fans complimented her looks

The 32-year-old, who is the current reigning French Open, US Open, WTA Tour Championships and Olympic ladies singles champion, also revealed she adopts a persona on court.

‘I think of myself as two different people,’ she said. ‘There’s the Serena Williams that everyone knows: She’s crazy. She can’t make a mistake.

‘And she’s angry and just not nice, to be honest. I’m only that person for three hours a day when I’m on the court. The rest of the time I’m just Serena. I’m the class clown.’

Keeping fit: As well as playing tennis, Williams goes running, cycles and has even tried yoga

However, Williams admits even she is shocked by the character she creates and said: ‘That’s when Serena Williams comes out and she’s nuts.

‘That really upsets me. It’s not the real me…. Even for me, it’s shocking to see.

‘But in another way, it’s kind of cool to know that I have everything together on the court, because I don’t really have my life together personally.

‘I’m here and there and everywhere traveling the world and playing tennis.’

Today Williams is the oldest player in history to be ranked world number one.

Early in 2011 she was hospitalised with a blood clot in her lungs, which nearly killed her.

She tells Fitness that for the first time she realised her health came first.

In character: Williams admits to adopting a persona on the court and is sometimes shocked by the character she creates

‘I realised that I’m really fortunate to be alive and to be playing, and that it’s not the end of the world if I don’t win … It was the first time I’ve ever had so much fun on the court. Now I know I don’t have to play again if I don’t want to. I play because I love it.’

After returning to the court, Serena set herself an impossible goal.

‘My goal was to be seeded at the U.S. Open by August [2011],’ she explained.

‘It was the first time that tennis was the last thing on my mind. I didn’t even think, I gotta practice because I’ve got to beat this girl… At one point, I was just thinking, Will I be OK?’

Public figure: Williams has revealed she learned to be proud of her curves after receiving compliments from fans

‘It’s virtually impossible to do that in three weeks. But I worked really, really, really hard with my trainer … It worked. I kept winning, and I was ranked 29th.’

As a result of her illness Williams overhauled all aspects of her life – including her diet.

‘It all started because I didn’t want to bring bad food into the house.

‘I live with my sister, Venus, who has Sjögren’s syndrome, an autoimmune disease. Before her problems I ate a lot of junk I also found out three years ago that I’m allergic to wheat, so I’m trying to eat a clean diet of natural, raw foods.’