The former Fame Academy hosts have been linked since they were spotted out on Valentine's Day in Los Angeles and holidayed together in Mexico.
Although neither have officially confirmed a relationship yet, sources say that Kielty revealed all to friends at the Electric House members' club in Notting Hill.
"Patrick was there talking to a group of friends when somebody asked him if there was a special lady in his life," the insider told the Daily Mail.
"He looked slightly sheepish and then said, 'Yeah, Cat'. When one of the men asked, 'Cat who?' he replied, 'Cat Deeley'."
A source close to Deeley told the Daily Star of the alleged relationship: "It's no secret among her friends that she's always held a torch for Patrick but it has never been the right time for either of them."
Deeley was recently named as a possible replacement for Steve Jones as host of The X Factor USA.