Hilary Duff Opens Up About 'Serious' Relationship With Ex-Boyfriend Jason Walsh

This video is unavailable because we were unable to load a message from our sponsors.

If you are using ad-blocking software, please disable it and reload the page.

Hilary Duff is talking about her romance with her former trainer, Jason Walsh.

The 29-year-old Younger actress called it quits with Walsh in November, five months after going public with their relationship. In her interview with Cosmopolitanfor its February cover, Duff reveals that she had actually been dating Walsh for a lot longer, and that it was "serious."

"We were seeing each other for a while," Duff tells the magazine. "People don't know the ins and outs of everything. It was definitely my first more serious relationship since my ex-husband [Mike Comrie]."

WATCH: Hilary Duff Says She's Not 'Desperate' to Find a New Boyfriend -- 'I've Never Been a Good Dater'

"I was like, 'F**k it. He's my boyfriend,'" she said about her decision to go public. "I just needed to make sure it was right. People don't need to know my business until I really know my business, you know?"

Though Duff admits their personal relationship affected their professional relationship.

"He's like, 'You don't listen to me anymore! I give up!'" she shares. "I have a different trainer now."

As for if her ex-husband knew about Walsh, Duff says she and Comrie -- who share a 4-year-old son, Luca, together -- always tell each other when they start dating someone.

"We feel like it's respectful to keep everybody in the loop," she explains. "I don't know as much about his life as he knows about mine because mine's a lot more public."


WATCH: Hilary Duff Steams Up Hawaiian Beach in Several Bikini Looks

Duff has already bounced back from her relationship with Walsh, and is now dating musician Matthew Koma. The two made their red carpet debut at Entertainment Weekly's pre-SAG Awards party at Chateau Marmont on Saturday night.

Watch the video below for more on Duff's new romance with Koma.