Hinting at whether a new bit of bling was on the cards for partner Dee Devlin, Tubridy said: "With all the money you'll be able to afford a ring for Dee now?"
To which McGregor replied "I know I shot myself in the foot when I said 'girlfriend'!" rubbing his hands together.
Last month the couple, who have been together for six years, celebrated their son's christening in a lavish party at Dublin's Luttrelstown Castle, complete with a mini-carnival and ferris wheel.
The interview will appear on The Late Late Show tonight. Other guests include Ibrahim Halawa, celebrity chef Nigella Lawson, chart-topping singer Imelda May and jockey Kieren Fallon.
The Late Late Show, RTÉ One, 9.35pm