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."