Miller reveals in a Wednesday episode of The Doctors that he suffers from Laryngeal cancer, with symptoms that can include a sore throat and ear pain. (Watch the clip exclusively on PEOPLE above.)
“A couple of years ago, we were filming [Flip or Flop] and my voice started to get scratchy,” Miller says.
El Moussa recalls how Miller began losing his voice and clearing his throat.
“It brought back memories of what I went through, which really scared me for him, which pushed me to make sure that he got it checked out,” say El Moussa, 36.
The HGTV host began raising money for his friend in June, when he shared a photo of Miller from a hospital bed.
“Our contractor Frank Miller from Flip or Flop is battling 2 very very aggressive cancers, really bad ones, he’s fighting for his life out of feeding tubes!!” El Moussa wrote. “His medical bills have become unattainable and we need your help to try and save Frank’s life…”
El Moussa donated $5,000 to Miller’s GoFundMe page. Of witnessing his friend battle with cancer, El Moussa says, “It was really, really difficult.”
“And as every day, week, month goes by I feel like it gets more and more [difficult] just to watch the process he’s gone through,” he continues. “I mean, he’s a beast. He’s been through so many radiation treatments, chemo treatments, he’s lost so much weight. But, I can say he’s a fighter. Absolutely.”
WATCH: Tarek El Moussa Says His ‘Number One Goal in Life’ Is to Be the ‘Best Dad’ as He Admits Fatherhood ‘Is Not Easy’
Four years ago, Tarek was diagnosed with both thyroid cancer and testicular cancer, but only revealed that he was battling the former.
“Testicular cancer is more of a private thing,” he previously told PEOPLE about why he kept it a secret.
See the full interview Wednesday on CBS (check your local listings).