Monica Raymund knew Casey and Sylvie would end up together on ‘Chicago Fire’

They were the couple no one saw coming.

Kara Killmer, who played paramedic Sylvie Brett on “Chicago Fire,” says that former co-star Monica Raymund knew Sylvie and Casey (Jesse Spencer) would end up together.

“Right before she [Raymund] left, she was the one who said, ‘They’re so going to put your characters together.’ And both of us were like, ‘Absolutely not,’ ” Killmer, 35, exclusively told The Post.

“She was actually the first person to predict Brett and Casey ending up together, so it’s pretty funny.”

Casey and Gabriela Dawson (Raymund) were fan favorites when the show debuted in 2012.

The pair, known as “Dawsey,” married in Season 5 before divorcing due to Dawson leaving for Puerto Rico. Raymund exited the franchise in Season 6, but would briefly reappear to wrap their storyline.

Casey and Brett began dating in Season 9 of the NBC series. After the pair broke things off in Season 11, things seemed pretty much over.

They tried to do long distance while Casey moved to Oregon to be the guardian of Andrew Darden’s sons, but failed. Casey later returned to “Chicago Fire” and married Brett in a Season 11 episode, which aired in February.

“I definitely was pushing it as hard as I could. And that’s kind of indicative of their relationship,” Killmer said. “And that’s what I like about their relationship the most. He kind of matures her and she makes him lighten up.”

Killmer, who joined in Season 3, said she was leaving “Chicago Fire” in November. Her last episode was Brett and Casey’s nuptials.

“I think this is a natural conclusion for my character,” Killmer told The Post. “I sort of am selfishly delighted over the fact that she started as a jilted bride.”

“One of the things that I’m the most grateful for is that 10 years is a long time,” she went on. “It is such a privilege to have spent 10 years in the storage space of first responders. Because we work hand in hand with real firefighters, real police officers, real paramedics, every episode, every single day. There is something very special about people who choose to be servicemen and women.”

Killmer wouldn’t mind returning for a guest appearance, however.

“The door is wide open. I mean, I’m happy to come back anytime. 51 is notorious for getting itself into all kinds of trouble,” she told The Post. “If they need Sylvie back anytime, any day. Happy to do it.”

Other actors who have left the show over the years include Alberto Rosende (Blake Gallo), Lauren German (Leslie Shay), Charlie Barnett (Peter Mills) and Yuriy Sardarov (Otis Zvonecek).

“We love homecomings. You can’t keep trotting out these big speeches about always being a part of 51 and then not make good on it. You know, I’m here,” Killmer said.

The hit drama is a part of NBC’s “One Chicago” universe.

“Chicago Fire,” in Season 12, follows the lives of paramedics and firefighters working at the Chicago Fire Department at the firehouse of Engine Co. 51, Truck Co. 81, Rescue Squad Co. 3, Ambulance 61 and Battalion 25.