Kaley Cuoco reunites with '8 Simple Rules' co-stars

(Instagram)

Kaley Cuoco, Martin Spanjers and Katey Sagal got together with Amy Davidson and her baby boy, Lennox, for a sweet "8 Simple Rules" reunion on Thursday.

"A little #8simplerules reunion party today with a tiny addition @kateylous @martinspanjers @amy_davidson#lennoxsawyerlockwood (someone is smiling down on us)," Cuoco captioned the black and white photo, referencing the late John Ritter. The show came to an end in 2005 after three successful seasons.

WATCH: 'Big Bang Theory' Welcomes Katey Sagal and Jack McBrayer as Penny's Family Members

Last month, it was revealed that Sagal will be joining the cast of "Big Bang Theory," where she'll once again be playing Cuoco's TV mom.

"Yes yes yes yes !!!" Cuoco posted to Instagram when the news was first announced, along with a throwback pic of herself and Sagal. "Once my tv mom, always my tv mom, love you@kateylous !!!!! #fullcircle."

"There will be a little reunion there, which we're excited about," Executive Producer Steve Molaro told ET's Kevin Frazier about the casting news. "She's going to be a little bit of a neurotic character because she's spent her life with her troubled son, Randall, who has been in and out of jail and has had some issues with dealing drugs. So we're going to start to dive into that."

WATCH: 'Big Bang Theory' Star Says Next Season Could Be Their Last