The 52-year-old actress opened up about her role as Ajak in the upcoming star-studded Marvel film, telling ET's Nischelle Turner at D23 Expo in Anaheim, California, on Saturday, how hard it was to keep this project a secret.
"I've known for a long time. I've known since March," said Hayek, who was also joined by co-stars Lia McHugh and Ma Dong-seok, of her casting. "We have to keep it a secret and it kills you. It's like the most amazing thing that can happen to you, but you cannot tell anyone."
In the Jack Kirby-penned comics, the Eternals are a race of beings created by the Celestials to protect the universe from the monstrous Deviants. The film also stars Angelina Jolie, Lauren Ridloff, Kumail Nanjiani, Brian Tyree Henry, Richard Madden and newly-announced Kit Harington.
Hayek, whose character is originally a man in the comic, said is she "kind of the leader" of the group and has a more motherly role.
"But Chloé [Zhao], the director, has approached the leadership a little bit more [with a] deeper connection," Hayek explained. "So it's like a family and I'm like their mother, and they're all beautiful in different ways."
As for what her 11-year-old daughter, Valentina, thinks of her being a superhero, Hayek joked, "Maybe she will listen to me now?!"
"She's very excited about it, but the most excited member of the family is, about this, was my husband [François-Henri Pinault]," she noted. "He loves the Marvel movies."
ET also spoke with Jolie on the red carpet, where she shared that she felt empowered putting on the costume for her Eternals character, Thena.
"You get the outfit on and then you see your kids and the way they look at you like, 'What are you doing?' Then you get nicely brought back down to Earth, like, 'You are so weird, mom!'" she said. See more of Jolie's interview below.