The British tv presenter (39) and Northern Irish comedian (45) welcomed their first child in January and managed to keep his name under wraps until Cat wore a necklace last week with her son's name.
But the So You Think You Can Dance host revealed it wasn't a "contrived" press opportunity, but rather they wanted to wait until the six-month-old had met his family in Ireland first.
The couple, who wed in Italy in 2012, flew to Ireland in May for a few weeks to catch up with the Kieltys in Co Down and after that, decided it was time to share it with everyone else.
"The reason we didn't say it beforehand actually was because he hadn't met all the other family - my husband is Irish and he hadn't met all their family yet in Ireland, so it felt weird to announce it to everyone when he hadn't met his granny and uncles and nieces," she told Access Hollywood.
"There was nothing contrived. It was cute though, right?"
"We got back in June....don't expect him on the red carpet anytime soon!"
The new mother gushed over her son to PEOPLE about her hopes for his future, saying: "I would like him to do anything he wants to do. I would like him to be happy, first and foremost.
"I would like him to be kind, I would like him to be funny and I would like him to be smart. And any of those things are fine by me."
The loved-up pair said they would be raising their son in California for the time being, but haven't ruled out a return across the pond in future.
"We're going to ensure we take the baby back home to visit our families as much as possible but, for now, we're happy here in Los Angeles and are excited to bring up our child with an outdoors lifestyle."
"They're going to experience the LA sunshine Patrick and I never got to experience."