When fans tune in to the "Dancing With the Stars" Season 25 premiere this Monday, they will notice Julianne Hough missing.

Hough started out as a pro dancer, and won her first two seasons on the show. She left as a pro after Season 8 and embarked on a singing and acting career, starring in "Footloose," "Rock of Ages" and "Safe Haven," among other films. She returned to DWTS as a guest judge, and then in 2014 as the permanent fourth judge. While judging the Monday night seasons, Hough continued to pursue an acting career, including starring as Sandy in Fox's live "Grease" musical last year.

According to Entertainment Tonight, Hough chose not to return to DWTS for the Fall 2017 season because she's working on other projects and focusing on her acting career.

The source who talked to ET emphasized that the decision had nothing to do with her recent marriage to hockey player Brooks Laich, since "she would never ever sacrifice her career for her husband." Besides, it looks like he's currently in camp with the L.A. Kings, as opposed to across the country, so his schedule wouldn't affect her DWTS schedule.

2017 Creative Arts Emmy Awards - Day 1 - Creative Arts BallThe source said that some folks around Julianne were surprised by her decision to leave her DWTS judging job, since it's "a consistent gig with a steady paycheck." Julianne has left DWTS before, including taking DWTS Season 22 off as a judge, and she could return again. "For Julianne, she is still on very good terms with everyone over at DWTS and no bridges were burned. Perhaps she'll be back in the future." DWTS pros do that pretty frequently, including her six-time pro champ brother Derek Hough, who is now judging "World of Dance."

So, at least for this season, we'll only see head judge Len Goodman, alongside Bruno Tonioli and Carrie Ann Inaba. A rep told ET they also "look forward to welcoming guest judges wherever possible."

DWTS Season 25 premieres Monday, Sept. 18 at 8 p.m. on ABC. Check out the fall celeb cast in the gallery below.

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