'Dancing With the Stars': Frankie Muniz Reveals Undiagnosed Memory Loss Condition

Actor Frankie Muniz made a surprising medical revelation on Monday night's episode of Dancing With the Stars.

This week's theme focused on contestants selecting a memorable year of their lives. Muniz selected 2017, because he has an undiagnosed memory loss condition. The Malcolm in the Middle actor said he doesn't remember many moments of his life, including key moments in his career.

He said he often has conversations with friends or former co-stars and he knows he was there, but simply can't recall what happened.

He said he hasn't received medical consultation on the condition, but he thinks the multiple concussions he's received in his life may have been a factor.

He also revealed his girlfriend details each day the couple spends together in a notebook to ensure Muniz can relive some of their happiest moments.

"I've learned to live in the present," Muniz said. "Even if I don't remember it all, I'm happy."

See some fan reactions to the emotional reveal below.

Wow. @frankiemuniz I did not know. I respected you before but now? Dang. Mis puros respetos. 👏👏👏👏 #crying #DWTS

— Julianna Stephanie (@julianna__steph) October 10, 2017

Frankie Muniz surprises@me every week, interesting to keep learning about him #dwts

— Jamie Abbott (@jlwolf21) October 10, 2017

That's kind of tragic. Asking a guy who has memory problems what his most memorable year is. #DWTS

— NotReality (@NotReality) October 10, 2017

Living in the present and wowing us with every dance! #DWTS

— Sarah Mathiowetz (@SarahHelen03) October 10, 2017

Dancing With the Stars airs Mondays at 8 p.m. EST on ABC.