Robert Downey Jr. has jokingly revealed his unborn baby is a boy.

The Hollywood star and his wife Susan Levin are expecting their first child together and the actor has seemingly confessed the tot's gender.

While speaking about his baby on the 'Tonight Show With Jay Leno', he said: "I am not permitted to discuss it. I keep dropping the ball everywhere - she [Susan] says, 'Don't tell your cousins', and then I tell them. I can't say a word."

Robert then shouted out, "we're having a boy", before covering his face in fake shame.

The 46-year-old actor - who has an 18-year-old son, Indio, from his previous marriage to Deborah Falconer - also told the chat show host when the baby is due.

He said: "It's due in late February."

Robert - who stars alongside Jude Law in the upcoming 'Sherlock Holmes: A Game of Shadows' - recently admitted he can't wait to meet his baby but he doesn't think he will work less when he becomes a father again.

He said: "Life is good. With a new baby on the way, maybe I ought to think about slowing down a little. But I can't see that happening in the short term."