Seth Green and Alyson Hannigan

Willow and Oz are getting back together! Well, sort of.

Seth Green, who played Alyson Hannigan character's high school boyfriend on Buffy the Vampire Slayer (you know, before she switched teams and became a witch) is set to guest-star on her sitcom How I Met Your Mother.

Catch up on full episodes of How I Met Your Mother

Green, 38, will play a "creepy" guy named Daryl who thinks Lily (Hannigan) and Marshall (Jason Segel) were his BFFs in college, according to TVLine. The only hitch? They barely remember the guy, and now he is obsessed with having them both in his life.

The episode is tentatively set to air on Dec. 10.

The Buffy co-stars have worked together before on the big screen in the '80s comedy My Stepmother Is an Alien. Green, the creator of Robot Chicken, is also known for his role in the Austin Powers films and as the voice of Chris on Family Guy.