Despite saying he's under strict instructions from his expectant wife to keep schtum, Robert Downey Jr can't seem to help himself.
The actor, who is currently promoting Sherlock Holmes: A Game of Shadows, told US chat show host Jay Leno that Susan didn't want anyone to know their baby's gender – and then proceeded to blurt out the secret.
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"I am not permitted to discuss it. I can't say a word," he said, adding: "We're having a boy!"
He then put his head in his hands, pretending to be horrified at the slip.
Robert's a bit of a joker so the whole thing may be a double bluff to put the press off the scent. Certainly, his other comments about his wife's pregnancy aren't to be taken seriously
Asked if he was having sympathetic symptoms, the actor quipped: "It's been tougher on me. Just the hormones and the moods stuff and the nausea, and the whole thing."
The baby will be a brother to Indio, 18, the star's son with ex-wife Deborah Falconer.
It's a little princess!