Robert Downey Jr. sang for guests at his 50th birthday party.

The 'Iron Man' star was treated to a performance from 'Hungry Like The Wolf' hitmakers Duran Duran before joining jazz rock band Steely Dan on the stage to belt out 'Reelin' in the Years'.

He said: ''It was kind of a big deal. What occurred was I had two bands. I had Duran Duran play and then they opened for Steely Dan. I was stoked.

''They said, 'Come up and sing ''Reelin' in the Years'' because we saw you sing that at a show once,' and I was like (shakes his head).''

However, things didn't go as well for Robert as he hoped because he found himself getting a bad case of stage fright.

Speaking on The Late Late Show with David Letterman Show, he added: ''I forgot the words because I was a little excited to be up on stage with Steely Dan.''

When asked if he froze, he added: ''No, I kind of lip-synced it to nothing.''

Meanwhile, Robert previously admitted reaching the milestone had made him feel more ''reflective and grateful''.

He said: ''I was really just more reflective and grateful. I got to be around all my loved ones, friends and co-workers.''