Robert Downey Jr. was nervous about becoming a father again.

The 'Marvel Avengers Assemble' actor - who already has son Indio, 18, with ex-wife Deborah Falconer - and wife Susan Levin welcomed son Exton Elias into the world two months ago and though the 47-year-old star was excited about having another child, he admits he had a lot of worries.

He said: "There was all this trepidation, all this projection, all this anticipation and goodwill and a good vibe about it.

"But what you're squeezing to the side - or what's in the glove box - is these thousands of forms of fear. And then he was born and they've all just kind of scattered now. It seems like he's always been here."

The 'Sherlock Holmes' star knows "anticipation and fear" are normal parts of parenting but thinks it is important not to project his concerns onto his offspring.

He told the new issue of Esquire magazine: "Am I going to know what to do with them? Does any new parent, even if you're not a first-time parent, ever really know what to do? Only thing you have to do, the only requirement, if you can hack it, is to not transfer your own discomfort in the moment to this fresh soul, right? You got to be mindful.

"I don't want to be so confident in myself. It's that balance between being relaxed enough to not be communicating anxiety and present enough to not be creating the very thing that you were anxious about by being so relaxed - because I've seen that parenting style, too."