Just last month, they took to social media to insist they were just good pals.
But a new snap of Kaley Cuoco and Johnny Galecki looking flirtier than ever has us thinking we're not quite getting the full story.
The Big Bang Theory co-stars, who did date back in 2009, were partying together in Los Angeles on Saturday night – and no doubt a few eyebrows were raised when Johnny posted this selfie to Instagram:
"Hilarious night out in the LA Arts District w/@normancook #BFFsbite," the actor wrote alongsid ea picture of him biting a laughing Kaley on the neck.
The pair are both free agents these days, after Kaley filed for divorce from her husband Ryan Sweeting back in September.
It's thought the couple's shock split was related to Ryan's addiction issues, in particular his dependence on prescription painkillers – something which only became an issue when he injured his back shortly after their December 2013 wedding.
But despite her ongoing flirty friendship with Johnny, Kaley has been keen to make it clear nothing is going on.
"So sorry to disappoint, but no home wreckers or secret flings going on here," she wrote next to a picture of herself and Johnny on Instagram three weeks ago.
"Me and @sanctionedjohnnygalecki are just the best of buds- Leonard and Penny will just have to suffice!!!"
Since when do the "best of buds" bite each other on the neck, though?