Jimmy got the bright idea to set up the duo on a faux Newlyweds-type game show, affectionately called The Newly X-Game, where the pair answered questions about one another separately before comparing answers to see how well they know each other.
The funnyman asked both Britney and Simon to reveal which body part they like most about the other. Britney giggled and held up her answer on a white card: "Chest Hair."
Britney, however, was in for a shock when Simon held up his card, which read "Her Tits."
The pair were in good spirits talking about the Fox show. Brit admits she loves being a mean judge, saying she would "want to know" if singing wasn't one of her great talents.
Meanwhile, Jimmy asked if there was any sexual attraction between the two on the set.
"It's a bit one-sided, Jimmy," Simon laughed. "From my side — Britney is engaged."
When asked about the wedding, Britney looked uncomfortable and refused to give any hint as to when she might get hitched. When Jimmy asked if it was a secret, she nodded.
Check out their Newly X-Game below!