Beyonce Knowles lost 20 pounds for her role in Oscar-tipped musical, 'Dreamgirls'.

However, the singer-turned-actress - who has been promoting the film at the Cannes Film Festival in France - felt the massive weight loss was the only to way to make her character convincing.

During a press conference, she confessed: "It was my idea. At the beginning of filming, I was my normal weight.

"I actually gained a little bit, but then I lost 20 lbs. when I went from young Deena to old Deena.

"I wanted it to be something more than just make-up and hair. I wanted to see the change."

However, Knowles, 24, said the film's director - Bill Condon - was worried she might be doing herself harm.

She revealed: "He actually kept telling me to eat, eat, eat for continuity, but I really wanted to go all the way. I was inspired by Tom Hanks.

"He did it all the way in the movie 'Castaway', so I said I can do it all the way!"

'Dreamgirls' focuses on Knowles' character Deena Jones, the lead singer of the Dreamettes - a '60s-style group loosely modeled on Diana Ross and the Supremes.

The movie - which is based on the award-winning 1981 Broadway musical - is due to be released at the end of the year and is already creating whispers of potential Oscar nomination.