"Personally, I'm a big fan of Katherine's husband, Josh Kelley, so kissing her in Life As We Know It was like indirectly getting to make out with him, " Duhamel, 37, tells Parade magazine, before adding: "Just kidding."
But Kelley wasn't crazy about watching his wife film a love scene.
"Josh didn't come around to the set during our big lip-lock," said Duhamel, "Katherine says he's never there when she has to do a make-out scene."
But on-screen kissing did serve as a source of jealously for one woman – and it wasn't Duhamel's wife, Fergie. It was Heigl.
"Katherine was like, 'You were making out with Katie Holmes in your last movie?'' – The Romantics – 'Excuse me, I'm already jealous,' " jokes Duhamel.
Duhamel's playful relationship with Heigl, 31, also extended to her daughter, 22-month-old, Naleigh, who had just been adopted at the time of shooting. "Little Naleigh was just a little sweetheart," says the actor, "She's so squishy and cute. She makes you want to chew on her cheeks."