John McCain's daughter shares emotional message after his cancer diagnosis

— -- Meghan McCain shared a moving message about her father shortly after news broke last night that the Arizona senator's doctors had found a brain tumor during recent surgery -- calling him her "hero" and saying "my love for my father is boundless."

Meghan McCain is known to have a close relationship with her father. Tissue analysis after a blood clot was removed from the senior Arizona senator's head revealed that he had glioblastoma, which has a five-year survival rate of 4 percent for patients over 55, according to the American Cancer Society.

A statement from the Mayo Clinic said: "Scanning done since the procedure (a minimally invasive craniotomy with an eyebrow incision) shows that the tissue of concern was completely resected by imaging criteria."

Meghan McCain shared her thoughts on her father's diagnosis in a screenshot posted on her Twitter account and later on her Instagram account.

The text of the message reads:

"The news of my father's illness has affected every one of us in the McCain family. My grandmother, mother, brothers, sister, and I have all endured the shock of the news, and now we live with the anxiety about what comes next. It is an experience familiar to us, given my father's previous battle with cancer - and it is familiar to the countless American families whose loved ones are also stricken with the tragedy of disease and the inevitability of age. If we could ask anything of anyone now, it would be the prayers of those who understand this all too well. We would be so grateful for them.

It won't surprise you to learn that in all this, the one of us who is the most confident and calm is my father. He is the toughest person I know. The cruelest enemy could not break him. The aggressions of political life could not bend him. So he is meeting this challenge as he has every other. Cancer may afflict him in many ways: but it will not make him surrender. Nothing ever has.

My love for my father is boundless, and like any daughter I cannot and do not wish to be in a world without him. I have faith that those days remain far away. Yet even in this moment, my fears for him are overwhelmed by one thing above all: gratitude for our years together, and the years still to come. He is a warrior at dusk, one of the greatest Americans of our age, and the worthy heir to his father's and grandfather's name. But to me he is something more. He is my strength, my example, my refuge, my confidante, my teacher, my rock, my hero - my dad. - MMM"

She wasn't the only one in the family to share support and personal memories online. Meghan's mother, the senator's wife Cindy McCain, posted a picture from their wedding in May 1980 on her Instagram account.

The caption reads: "Thank all of you for the wonderful thoughts. @senjohnmccain is doing well. We as a family will face the next hurdle together. One thing I do know is he is the toughest person I know. He is my hero and I love him with all my heart."