Selma Blair's Son Arthur, 11, Says He's 'Really Proud' of Mom After DWTS Debut: 'It Was Amazing'

Selma Blair had her biggest fan by her side when making her Dancing with the Stars debut this week.

On Monday night, the Legally Blonde actress, 50, took the stage with pro dancer Sasha Farber, bringing fans and the judges to tears with her moving performance.

Blair, who has been open about her MS diagnosis and how she hopes to make a statement on the show, danced an elegant routine to David Cook's "Time of My Life."

After the performance, which earned the pair a 28/40 from the judges, Blair's 11-year-old son Arthur, whom she shares with ex Jason Bleick, raved over his mom's routine.

"I'm really proud of her," he told Access Hollywood. "It's just wonderful that she does this stuff and moves around."

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

ABC/Eric McCandless

RELATED: Selma Blair Says She 'Had No Idea I Had Hope' Until Son Arthur's Birth: 'I Didn't Look for My Own'

"It was amazing," he added. "Even the judges were moved by it."

Ahead of her routine, Blair and her partner spoke about her MS diagnosis in her introduction package, noting how she struggles with her physical and mental abilities.

"I want to perform in a way that uses my body," she told Farber in rehearsals. "Doing this can only help me in the long run."

Blair also admitted that she was feeling nervous about her balance but noted, "I've underestimated me in the past so don't underestimate me."

Selma Blair/Instagram

Last month, the Cruel Intentions actress shared a car selfie with son Arthur on his first day of fifth grade. The tween smiled in a navy hoodie as he looked up at the camera.

"I almost didn't get a picture with the fifth grader!" she captioned the sweet shot. "I am proud of you Arthur. Proud you even got out of the car 💁🏼✨🥇🤪."