Kielty began performing regularly while a pupil at St Patrick's Grammar School, Downpatrick, which holds an annual holiday concert.
Kielty was persuaded to take part by a Games master who spotted his impersonations of local politicians, celebrities, and sportsmen.
Speaking for the first time about their relationship, Cat said: ""I am no longer a single lady. I have known him for 10 years."I don't know [why it took so long].
Patrick Kielty is grateful there was no ''awkward dating'' for himself and Cat Deeley.
He said: "We call [Milo] the Fresh Prince of Bel Air because he gets whatever he wants.
"You suddenly realise when you get married, you're number one.
One routine performed a local gigs involved donning a balaclava and making spoof paramilitary pronouncements. He later became the warm-up act for a BBC Northern Ireland programme, Anderson on the Box, presented by local personality Gerry Anderson.
He said: ''We call [Milo] the Fresh Prince of Bel Air because he gets whatever he wants.''You suddenly realise when you get married, you're number one.
His professional career started while he was still a psychology student at Queen's University of Belfast.
called "The Empire Laughs Back" started by him and fellow student Jackie Hamilton, who went on to become a BBC producer.
Then a kid comes along and you're number two, then a dog you're number three and you spend your life going down the pecking order.''Patrick also spoke about how he ''pretends'' to have work commitments in the UK, just so he can have some relief from family life on flights to and from the US.
Kielty was born in Downpatrick, Co Down, Northern Ireland, and grew up in the neighbouring village of Dundrum.