Michael Strahan's daughter Isabella has been diagnosed with a brain tumor.

The father-daughter pair revealed Isabella's diagnosis with medulloblastoma on "Good Morning America" Thursday with host Robin Roberts.

"I didn't notice anything was off till probably like Oct. 1," the 19-year-old said. "That's when I definitely noticed headaches, nausea, couldn't walk straight." Eventually, she said, she began to dread waking up because she was throwing up.

Isabella's twin sister Sophia encouraged her to seek treatment and Isabella received her diagnosis in October following an MRI.

One day before Isabella's 19th birthday, she had surgery to remove the tumor, which was slightly larger than a golf ball.

Isabella was on the West Coast, where she was beginning her freshman year at the University of Southern California in Los Angeles, while Strahan, who co-hosts "GMA" and "NFL Sunday," was in New York at the time of his daughter's surgery.

"The hardest thing to get over is to think that she has to go through this herself," Strahan recalled. "Doctors said, 'You shouldn't risk trying to put her on a plane to get her to the East Coast or to another doctor. We know what it is and we should get it out as soon as possible.'"

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What is medulloblastoma?

Medulloblastoma is a cancer that typically develops in the cerebellum, the back of the brain responsible for movement and motor skills, according to the National Cancer Institute.

The cancer type is most commonly found among children.

Michael Strahan's absence from 'GMA' occurred while daughter Isabella was recovering from tumor surgery

Strahan was absent from his hosting duties for three weeks at the end of October into November due to "some personal family matters," an ABC spokesperson told USA TODAY in a statement. Up until today, he had not gone into the details of his absence.

The NFL player turned host is a father to four adult children. He shares Tanita, 31, and Michael Jr., 28, with his first wife Wanda Hutchins. He also shares 19-year-old twins Isabella and Sophia with his second wife Jean Muggli.

Isabella finished radiation therapy on Wednesday and will begin chemotherapy in February, she shared Thursday.

The college student and her father also discussed how this has impacted their perspective on what is important in life.

"You learn that you're probably not as strong as you thought you were when you have to really think about the real things, and I realized that I need support from everybody," Strahan said. "You think that I'm the athlete, the tough guy, you know, I can come and handle, I'm the father in the family. It is not about any of that. It doesn't matter. And it's really made me change my perspective on so many things in my life."

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Isabella added: "I'm grateful. I am grateful just to walk or see friends or do something, 'cause when you can't do something, it like, really impacts you."

As for the future, she said, "I'm looking forward to getting back to college and moving back to California and just starting my school experience over. Not over, but just restarting, being back into a routine and something that's enjoyable."

"Today my daughter @IsabellaStrahan joined @RobinRoberts and myself for an interview about the journey she has been going through on @GMA," Strahan wrote on Instagram. "I love you Isabella and I’m always by your side. To all sending love, we thank you from the bottom of our hearts!!"

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