Isabella Strahan is opening up about a heartbreaking medical diagnosis.

Michael Strahan's 19-year-old daughter shared she has been diagnosed with medulloblastoma, a malignant brain tumor found in children.

"I didn't notice anything was off till probably like Oct. 1," she told ABC News' Robin Roberts in an interview alongside her dad Jan 11. "That's when I definitely noticed headaches, nausea, couldn't walk straight."

Though Isabella assumed she had vertigo, later that month her health took an even more unexpected turn.

"I was throwing up blood," Isabella recalled of one afternoon. "I was like, 'Hm, this probably isn't good.' So I texted [my sister], who then notified the whole family."

And after her symptoms continued, her dad Michael insisted they look into her health further.

"That was when we decided, 'You need to really go get a thorough checkup,'" the Good Morning America host shared. "And thank goodness for the doctor. I feel like this doctor saved her life because she was thorough enough to say, 'Let's do the full checkup.'"

After completing an MRI, Isabella received a life-changing call.

"She calls me and she's like, 'You need to head to Cedars-Sinai [Medical Center] right now,'" she shared of her physician. "I'm gonna meet you there.'"

Michael—who took a step back from his hosting duties in November—shared he learned about the diagnosis before his daughter, adding that "it didn't feel real."

"I don't really remember much," he noted. "I just remember trying to figure out how to get to L.A. ASAP. And it just doesn't feel real."

The former athlete, who shares Isabella and her twin sister Sophia with ex Jean Muggli, went on to explain that Isabella's type of tumor is rarely found in someone around her age.

"But it's still scary because it's still so much to go through," he continued. "And the hardest thing to get over is to think that she has to go through this herself."

In late October, Isabella underwent emergency surgery to remove the mass, sharing that she has recently finished radiation therapy.

"I got to ring the bell yesterday," she said. "It was great. It was very exciting because it's been a long 30 sessions, six weeks."

However, Isabella explained that she's still in the process of treatment and will start chemotherapy next month.

"That's my next step," she added. "I'm ready for it to start and be one day closer to being over."

Amid her recovery, Isabella is also looking forward to her future. "I'm looking forward to getting back to college and moving back to California and just starting my school experience over," she said. "Not over, but just restarting, being back into a routine and something that's enjoyable."

And for Michael, the process has given their family perspective.

"I literally think that in a lot of ways, I'm the luckiest man in the world because I've got an amazing daughter," he noted. "I know she's going through it, but I know that we're never given more than we can handle and that she is going to crush this."