Ben Affleck's son's birthday party was more emotional than anticipated.
ET's Nischelle Turner caught up with Affleck at the premiere of his latest flick, Triple Frontier, where the 46-year-old actor dished all about his son Samuel's How to Train Your Dragon themed 7th birthday party. At the fun-filled event, Jennifer Garner, Affleck's ex-wife and Samuel's mom, dressed up as Astrid, the leading lady in the movie. However, it was a move that did not earn her praise from her embarrassed son.
"I was shocked as anybody when I saw Jen come out as Astrid," he admitted. "But then she said Sam was like, 'OK Mom. We already have an Astrid.'"
Though Affleck "didn't go to quite those extremes" in the costume department, he did "participate in a very heavy viking themed How to Train Your Dragon birthday extravaganza," and felt bad that Samuel didn't appreciate his mom's extra effort.
"I felt so bad. She was devastated," Affleck continued with a good-natured laugh. "She had gone to all these lengths to put on the costume."
"We're just not that cool," he added.
Garner first revealed Samuel's reaction to her costume in an Instagram post last week. In the pic, she showed off her fur boots and a matching shawl, along with some leather armor and blue face paint, which made her look like the spitting image of Astrid, who was voiced by America Ferrera in the movie.
"Well, guess what. It turns out seven is the age my kid stops thinking it’s cool when I dress up for the party," Garner captioned the shot before adding hashtags reading "youngest child," "first eye roll," and "anyone need an Astrid?"
In addition to Samuel, Garner and Affleck share two daughters, Violet, 13, and Seraphina, 10. Despite still co-parenting, the formerly married couple have each moved on romantically; Garner with boyfriend John Miller, and Affleck with his potentially former ex, Lindsay Shookus.
Affleck and Shookus have been spotted out and about as of late, following their split six months ago. A source recently told ET that the pair are "hanging out again" and have been "for over a month now."
Triple Frontier hits theaters March 6 and lands on Netflix March 13.