Reunited as Guest Star

Two actors were on a show together. Some time later, one actor gets a new show and their old castmate makes a cameo.

1. Katey Sagal & Christina Applegate, Married With Children ---> Dead To Me. Katey Sagal and Christina Applegate played mother and daughter on Married With Children in the 80s. In 2020, Katey guest-starred on Christina's new show "Dead to Me", playing Linda Cardellini's mom. However, Katey and Christina wouldn't share a scene for another season. 2. Katey Sagal & Kaley Cuoco, 8 Simple Rules for Dating My Teenage Daughter ---> The Big Bang Theory. Once again, Katey played a mom, this time to Kaley Cuoco on 8 Simple Rules in the early 00s. Many years later, Kaley Cuoco was one of the stars of The Big Bang Theory. When it came time for Penny and Leanord's wedding, and Penny needing a mom, they hired Katey to play her. (This one is a little bittersweet because you're left wondering if John Ritter had lived if he would've played her dad. Instead, the role was played by Keith Carradine) 3. Jonny Galecki, Sarah Gilbert & Laurie Metcalf, Roseanne ---> The Big Bang Theory. Johnny Galecki played Sarah Gilbert's boyfriend, later husband, and Laurie Metcalf's nephew-in-law on Roseanne back in the 90s. He also dated Sarah Gilbert behind the scenes until she realized she was a lesbian. Later, he was also one of the stars of The Big Bang Theory. Both Sarah and Laurie had roles in different seasons where they interacted, with Sarah playing one of his girlfriends. Though I don't think Sarah and Laurie ever shared a scene. 4. Kevin James & Leah Remini, King of Queens ---> Kevin Can Wait. This one was controversial. Kevin and Leah played husband and wife on King of Queens. Years later, Kevin was helping put together a new sitcom for himself, Kevin Can Wait. Story goes, he did initially want Leah to play his wife but something prevented it from happening, so Errin Hayes was hired. Leah had a guest spot in S1 and the chemistry was still there. So...the show killed off Errin's character in S2 and promoted Leah to starring. While the two characters didn't get together before the show was cancelled, it was clear that was the direction it was heading in. Court of public opinion was split, but many were on Errin's side. Part of this is what inspired the show "Kevin Can F\*ck Himself".