Robert Downey, Jr.: "We're Having A Boy!"

It's a boy for Robert Downey, Jr. and wife Susan Levin!

The Iron Man star, 46, spilled the beans about the sex of the couple's unborn baby during an appearance on The Tonight Show, at first telling host Jay Leno, "I am not permitted to discuss it... I can't say a word," before announcing, "We're having a boy!"

Levin is due in "late February," but according to Robert, if these next few months are anything like the rest of her pregnancy, it may be harder on him than the mom-to-be.

"I don't wanna be presumptuous," he joked. "But I think actually [the pregnancy] has been tougher on me [than Susan!]... Just the hormones and the mood stuff and the nausea and the whole thing.

"I gotta be careful," the actor added. "I am gonna have to see my wife some time after doing this segment with you, and I think I'm already in trouble."

Already dad to 18-year-old son, Indio, Downey, Jr. says that he plans to be very involved with baby number two, even when it comes to diapers.

"That's just poop," Robert quipped. "That's no big deal."