Kaley Cuoco isn't the only "Big Bang Theory" star who has a history with Johnny Galecki.

The cast of the hit CBS show appeared altogether on Wednesday's Conan, and things got a little awkward when the host brought up Mayim Bialik's on-screen kiss with Galecki when they were both on the hit '90s sitcom, Blossom.

WATCH: Mayim Bialik Flashes Piers Morgan in Response to Susan Sarandon's #CleavageGate

The actors were just 14 when they shared their first on-screen smooch. "It might have been my first real-life kiss also," Bialik admitted.

"Do it again!" urged their Big Bang Theory co-star, Kunal Nayyar. Jim Parsons further quipped, "What kind of show is this?"

PHOTO: Mayim Bialik Shares Amazing Throwback Photo With Jennifer Aniston

Bialik and Galecki eventually gave in and recreated the kiss, and they've certainly improved over the past decades.

Going along with the gag, Parsons and Cuoco also attempted an on-screen lip lock.

WATCH: Kaley Cuoco Says She's in a 'Much Better Place' Since Split From Ryan Sweeting

It's no secret that Galecki and Cuoco dated when Big Bang Theory first started, but after the actress announced her split from husband, Ryan Sweeting, a new crop of romance rumors spread about the co-stars. "So sorry to disappoint, but no home wreckers or secret flings going on here," Cuoco responded via Instagram to the reports in January. "Me and @sanctionedjohnnygalecki are just the best of buds -- Leonard and Penny will just have to suffice!"