"Yeah, we're very much in love, especially her," the Scottish hunk said on Thursday's Tonight Show With Conan O'Brien, when asked about the rumours. “And I'm making an announcement here that we're actually going to tie the knot next Tuesday or Wednesday."
If there was any uncertainty about whether or not he was joking, his next comment soon cleared it up.
"Then I'm marrying Cameron Diaz. And who else? Joan Rivers will be the next weekend, then fill out the applications for the next one because all comers are welcome," he joked, before finally saying: "It's not true, of course."
Reports of a romance began to surface after Jen was spotted with her arm around Gerard between takes of filming their joint project The Bounty in New York.
And on-set sources say the 40-year-old actress, who recently split with musician John Mayer, has revelled in spending time with her handsome co-star.
"There's a definite chemistry between Jennifer and Gerard," says the source. "They seem to be spending a lot of time together, even when they are not working."