Will.i.am would love to work with Robert Downey Jr. as he's got "crazy gymnastic skills" when it comes to his singing voice.

The Black Eyed Peas rapper has collaborated with a string of big names in the business, including Michael Jackson, Britney Spears, Justin Timberlake and Usher. The next star on Will.i.am's wish list is actor Robert.

"I would like to work with Robert Downey, Jr.. That guy sings. I was at this thing at a 60th birthday party in New York, so I was just sitting there, I'd done my song and I was nervous I got cotton mouth, that's the first time I got cotton mouth in a long time. You could pull a T-shirt out of my mouth," he laughed in an interview Access Hollywood Live's Billy Bush and Kit Hoover.

"I did the show, it was cool, and then I'm sitting in the audience watching, and I was like Who is that singing?'" he recalled, before realising that it was in fact Robert.

"I told him, You were so crazy, super-fresh, with it. Dumbalicious'. He's got crazy gymnastic skills with the vocals."

Will.i.am was a friend of Michael Jackson's before the superstar died in 2009. The star says his relationship with the King of Pop was one of the biggest highlights of his life.

"My moment was working with Mike, seeing Mike, and being his friend," he gushed, before explaining their close friendship in more detail.

"He would call me late. We would talk on the phone, he would call me for Father's Day, call me on Mother's Day, birthdays, things like that so it surprised me just how down to earth as big as he is how down to earth he was."