Rapper will.i.am shunned fanfare to celebrate his 38th birthday with a low-key soup and salad meal - because he's on a strict diet.

The Black Eyed Peas star turned 38 this week (15Mar13) but instead of throwing a huge party, he invited his pals to feast on healthy food with him on Thursday night (14Mar13).

On a whim, he decided on his birthday the next day (15Mar13) to unveil his latest single, #ThatPower, featuring Justin Bieber, at London-based radio station Capital Fm.

He told the station's Djs, "Yesterday I had a birthday dinner. We just had some dinner and I'm on a soup and salad diet so I just had some soup and salad...

"Today is actually my birthday. Everybody was like, 'Let's have a party!' I don't like celebrating my birthday, I don't like having parties, so I was like, why don't we just have some dinner, have some soup and salad and then not go to sleep and then hang out at the Capital Fm lobby? That was what we wanted to do. I think that's a good way to start my birthday, just go down to Capital Fm, I swear to you. So that's what we did. We were like, let's go by Capital and play some music. That would be fresh."

will.i.am went on to reveal how his collaboration with Bieber came about, adding, "Actually we went shopping first and we were like, 'Hey, let's just have a chilled day' and we went shopping for shoes, then after that we went to the studio, watched the BRITs (Awards), recorded that and then trucked off to see Justin Timberlake perform. So that was a pretty full day."