Affleck, who will star as Batman in the upcoming "Batman v Superman" film, told Kimmel that Samuel had requested a superhero themed birthday party, and one of the superheroes that his son wanted present at the party was none other than Batman himself.
“He wanted a superhero birthday party and so he wanted superheroes there,” Affleck said. “He was like, ‘and I want you to do Batman. Real Batman!'"
Affleck admitted that he had to convince the studio to let him borrow the Batman costume for the birthday party, and joked that he had to "sign [his] life away" in order to use the costume for the party.
The 43-year-old actor stated that while he didn't mind dressing up for the kids at the party, it was "mortifying" to have to portray Batman in front of the children's parents.
“There was Wonder Woman, Captain America, Iron Man and there was me … it was so mortifying,” Affleck said. “First I thought, ‘It’s kids. It’s kids.’ I didn’t think that, of course, like, all their parents are there."
“So I had to, like, put on my outfit for this movie, and put on my scary face for the 4-year-olds and all their folks are there," he continued. "It’s 11 in the morning and they’re kind of like ‘Wow. Batman.'”
The actor then mimicked his deep and raspy Batman voice while explaining himself to the parents, saying, "This means a lot to my son. Don’t make me come find you.”
Watch part of Affleck's appearance on ""Jimmy Kimmel Live!"" below: