Robert Downey Jr. Reveals the Meaning Behind Son Exton’s Name — and Shares Baby Photos!

When Robert Downey Jr. welcomed his son Exton in February, people wondered how exactly he and his producer-wife Susan Downey came up with the baby's name, which is not something you'd hear at the playground all that often. Was it a place name? (There are Extons all over the map and the actor did name his 18-year-old son Indio after the California city where the Coachella music festival takes place.) Or perhaps those Jolie-Pitt boys inspired another "x" name? (Maddox, Pax and Knox are mini trendsetters, you know.) Well, we have finally have the answer courtesy of Downey himself.

On the "Tonight Show with Jay Leno" on Thursday night, Downey, 47, explained the name meaning, saying: "My wife's great uncle was kind of eccentric. He lives in Madison, Wisconsin. When he was in the fourth grade he realized he didn't have a middle name, so he changed his name [to include Exton]."

Downey told Leno that the last time he was on the show, he got into trouble with his wife, who was pregnant at the time, for revealing the gender of their child on TV because they had previously decided to keep it a secret.

[Related: Robert Downey Jr. Was Terrified Before Son Exton's Birth]

"I wasn't supposed to reveal the sex. When I got home it was not a really happy moment," Downey said, before adding, "Honestly, it wasn't that bad." He said as long as he didn't do anything crazy during this appearance on the show — like, perhaps, show a photo of the child on TV — all would be forgiven with his wife. "I'd get in huge trouble" if I showed a photo of Exton, he said, before quickly changing his mind and saying, "Well, if you want me to I will."

The actor, whose latest movie "The Avenger's" opens today, then showed a precious photo of Susan holding Exton and giving him a gentle kiss on his head. In the picture, the first-time mom is wearing a necklace with the baby's name on it. Then Downey shared a second photo of the little guy, who was dressed in a striped sweatshirt and orange pants.

"He's so darn cute isn't he?" said the proud dad.

[Related: 'Avengers' Hurtles to $178.4M Overseas Debut]

So how is fatherhood different this time around? Downey said it's a completely new experience, especially now that he's sober after a long battle with drug addiction. "Well I find it easier," he admitted. "I'm not smoking pot [all the time], which [makes it] difficult when you're changing a diaper and you're stoned."

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