The former Friends actress was seen on camera in the audience sitting alongside the couple's daughter Coco following Arquette's first-ever performance on the dance floor.
Speaking to co-host Brooke Burke backstage about Coco, Arquette said: "It's just so beautiful to see her. She's the light of my life and I'm just happy she is here.
"I love her so much."
Arquette and his professional partner Kym Johnson earned 18 out of a possible 30 points from judges Len Goodman, Carrie Ann Inaba and Bruno Tonioli for their Viennese waltz.
The actor previously told US Weekly that Coco was "excited" to see him performing but also "a little worried" that he might embarrass her.
"I look forward to when maybe she gets past the embarrassment," he added. "Maybe she'll want to learn a few moves with me! I'd love to dance with her and have her be a part of this."
Arquette and Cox separated in October 2010, although they have remained friends.
Dancing with the Stars airs Mondays and Tuesdays on ABC. It premieres Monday, September 26 on Watch in the UK.
> Read Digital Spy's full recap of this week's Dancing with the Stars performances