And while the couple welcomed their two tykes on June 6, with Father's Day right around the corner, Nick hilariously revealed that he shared with his son the blunt truth about the holiday.
"I was explaining to George on this holiday thing, that Father's Day is pretty much of a minor league holiday and he is going to have to get used to that," Nick shared. "As long as he didn't get the stretch marks, he doesn't get the adulation."
"Mother's Day is a big deal, Father's Day is just a supporting character," he added.
Still, Nick said he has seen a changed man in his son ever since the actor first found out he was going to be a dad.
"Since the word came out that he was going to be a father, no question about it, he changed," Nick explained. "This has nothing to do with age, but this is a different kind of maturity. When you figure out that you're going to take that standard responsibility that everybody else has done for years, and now you're on the merry-go-round. You're in the middle."
One thing that this sort of maturity entails -- a lot of sleepless nights.
"I suspect, and i can't verify this," Nick said, "he will not get any standard rest until about December 15."
And it's important to Nick to give Amal and George the time they need to adjust to their new reality.
"I'm going to stay as far away as possible until they get some kind of an idea of what this is all about, and they're in the midst of doing that now," he said. "They deserve as much quiet time and private time as possible."