The "Bad Moms" actress was fine with Kutcher trekking to space, until they had children and she persuaded him to stay put.
"I know I hate it," she tells People.com of her decision now. "Also I'm such a 'Star Trek' fan. The fact that I didn't let him go into space was so selfish of me, but I was a new mom and I was like, 'You can't leave me and the babies.' And so that's where that decision was made out of."
The "That '70s Show" star bought the ticket from the British entrepreneur years before the couple welcomed daughter Wyatt Isabelle, now six, and son Dimitri Portwood, four.
"I want everybody to know I probably would have let him to go to space now, but now it's too late [sic]," Mila adds.
Ashton opened up about Mila's role in him giving up his ticket in an interview with Cheddar News.
"When I got married and had kids, my wife basically encouraged that it was not a smart family decision to be heading into space when we have young children," he recalled. "So, I ended up selling my ticket back to Virgin Galactic. I was supposed to be on the next flight, but I will not be on the next flight."
Branson first blasted off in his own spaceship on July 11, beating fellow billionaire and Amazon boss Jeff Bezos into outer space.