The 46-year-old actress dedicated a post to Vartan, her ex-boyfriend and former co-star, on the actor's 50th birthday Tuesday.
"Can you believe this baby face is 50?! Happy birthday, #MichaelVartan. #alwaysanALIASgirl #sydneyandvauhgnforever," Garner captioned the post on Instagram.
"I don't think so. If it didn't work once, there's a reason it didn't work," the star said.
"Everyone's realizing that it is so much easier to be single," he later added. "I love relationships... when they work. When they're great, they're great and they're not, they're not."
Vartan split from Lauren Skaar in 2014 after three years of marriage, while Garner separated from Ben Affleck in 2015 after 10 years of marriage.
Alias had a five-season run from 2001 to 2006. Garner discussed reboot rumors with The Hollywood Reporter in October, saying she would be "very, very angry" if she didn't have a guest spot on the new show.