After Ballas and Milian, a singer and former The Voice social media correspondent, took the stage and performed a foxtrot routine, Hough offered up some advice and seemingly unwanted criticism.
"There were moments where I felt like choreography-wise, it was like two people dancing side-by-side rather than together," Hough told the couple during the show. "And I really want to see [Christina] shine. So, I've danced with Mark. You have to stand in front to make sure you're seen. So I really want Christina to shine next week if you guys are still here."
Hough, Milian, and Ballas all laughed it off, but it was clear there was tension in the room and people were surprised by the remark. Ballas tried to uphold a forced smile and then Milian enthusiastically replied, "We shine together."
After the show, Ballas fired back at Hough.
"The one comment for me that was a little funny is that I make it all about me... All the critiques were at me, and not at [Christina]. So I thought that was a little hypocritical comment," Ballas toldUs Weekly.
"I think [Julianne] was very insightful tonight though and gave great tips on lines and how to express. We've had a lot of guest judges and I thought out of all of them she was one of the best. So that part, I love. I was the one who kind of got the heat, but you know what, that's OK! It's fine."
Ballas and Hough are former childhood friends and dance partners, as the actress and her brother Derek Hough had both moved to London in the 1990s to train with Ballas' parents Shirley and Corky Ballas.
During last night's Dancing with the Stars show, Ballas and Milian finished in a tie for fourth place with three other celebrity and professional pairings. They earned 24 out of 30 possible points from the judges.