On Nov. 9, Hannigan tweeted behind-the-scenes pictures with her pal on the set of CBS' How I Met Your Mother. "I'm in the makeup chair again and next to me is Seth Green. Yay!" the 38-year-old wrote. "Reunited and it feels so good!"
Green, 38, responded by uploading a picture of himself with Hannigan on his WhoSay account. "Spending the day with my favorite costar," he wrote in the caption. Hannigan then tweeted a picture of Green bonding with her 5-month old daugher, Keeva. (The actress is mom to daughter Satyana, 3, with husband Alexis Denisof.)
Green will play Daryl LaCoutre, a former Wesleyan classmate of Hannigan's character, Lily Aldrin. The episode is slated to air in December.
Before Green left Buffy the Vampire Slayer during the show's fourth season in May 2000, his character, Daniel "Oz" Osbourne, dating Hannigan's Willow Rosenberg. She later began dating a witch, Tara Maclay (Amber Benson).
Since the show ended after seven seasons in 2003, Robot Chicken co-creator and voice actor Green married actress Clare Grant on May 1, 2010. Hannigan, meanwhile, has enjoyed career success in both film and TV, thanks to roles in the American Pie franchise, Veronica Mars and Date Movie.
This article originally appeared on Usmagazine.com: Buffy the Vampire Slayer Costars Alyson Hannigan, Seth Green Reunite on How I Met Your Mother Set