Carlos Barria / Reuters Meghan McCain introduces her father, then-Republican presidential nominee John McCain, during an Ohio rally in 2008.

Meghan McCain, daughter of Sen. John McCain (R-Ariz.), tweeted a message of heartbreak and hope on Wednesday, following the news of her father’s brain cancer diagnosis.

Meghan McCain, a co-host of Fox News’ “Outnumbered,” said that the entire McCain family was shocked to learn of the diagnosis and asked for prayers, but she also wrote candidly of her father’s confidence and strengths.

“He is the toughest person I know. The cruelest enemy could not break him. The aggressions of political life could not bend him,” she wrote.

“Cancer may afflict him in many ways: But it will not make him surrender,” McCain continued. “Nothing ever has.”

Sen. McCain was diagnosed with brain cancer less than a week after he underwent surgery at the Mayo Clinic Hospital in Arizona to remove a blood clot from above his left eye, according to a statement from the hospital. A subsequent pathology report found that the blood clot was associated with a brain tumor known as glioblastoma.

Doctors said Wednesday evening that McCain was “recovering from his surgery amazingly well” and called his underlying health “excellent.”