Jodie Sweetin posted what she thought was an innocent birthday message to her "Full House" co-star John Stamos. But when a fan replied with a "nasty" rumor about the pair, Sweetin quickly clapped back.

"Happy Birthday, Uncle J! My, my...we've made quite the memories these last 30+ years!" Sweetin wrote Sunday. "I can't believe you're about 10 years younger than I am currently in this photo!! We were babies! (Well, I actually was...haha) Love you so much."

That's when a fan commented, "How can you still say uncle to him when it's been reported that you slept with him?! That's just nasty."

The 36-year-old actress replied, "Hahahah...um...what?! Yeah that's def not true."

The co-stars acted alongside together as Stephanie Tanner (Sweetin) and Uncle Jesse (Stamos) on the hit series "Full House" from 1987-1995. They later reprised their roles in Netflix's reboot "Fuller House."

As for their love lives -- Stamos recently welcomed son Billy with wife Caitlin McHugh and Sweetin is dating Mescal Wasilewski.