Sir Paul McCartney is writing a ballet.

The former Beatle - who is one of Britain's most successful music stars, selling 100 million singles in the UK - has already begun work on the project, but he is unsure what writing the ballet will entail.

He told The Sun newspaper: "I'm interested in doing things I haven't done before.

"That offer came up and I love writing music. The two went together and I said, `Yeah.' I accept things before I know what I'm doing. I don't know that much about it yet."

The ballet is yet another musical departure for Paul who has released electronic albums, written classical music and film soundtracks.

The 68-year-old musician recently performed hit tune 'Ebony and Ivory' alongside Stevie Wonder for US President Barack Obama and he admits it was a "humbling" experience.

He explained: "Me and Stevie Wonder sang 'Ebony and Ivory' and that was like the first time we'd done it live.

"It brought back memories of when I wrote it, and when we recorded it. There was no chance of having a black president. I mean, it was just the remotest thing ever, so to be there, singing it with Stevie, and two yards away from the black president, his wife and kids, it was very emotional actually. So yeah, I was humbled and grateful."