After undergoing surgery to remove a blood clot, Senator John McCain's doctors announced on Wednesday (July 19) that they had discovered inside the Republican senator an aggressive form of brain cancer. Following the revelation, country star Tim McGraw was one of many to reach out on social media and offer up prayers for the veteran and politician.

"A real good man and A REAL HERO," McGraw writes on Instagram, also sharing a photo of McCain, 80, during his military days. "Prayers from the McGraw family, @senjohnmccain."

McCain's unexpected diagnosis came after doctors discovered the blood clot during a routine physical checkup. McCain displayed no symptoms, doctors say, and although they have fully removed the cancerous cells, McCain has glioblastoma, which is one of the most common but most malignant types of brain tumors; glioblastoma is treated with chemotherapy and radiation, but it often grows back.

“The Senator and his family are reviewing further treatment options with his Mayo Clinic care team," a statement from the office of Senator McCain reads. "The Senator’s doctors say he is recovering from his surgery ‘amazingly well’ and his underlying health is excellent."

McCain served in the Navy from 1954 until 1981 and was taken prisoner 50 years ago, in 1967, when the plane that he was piloting was shot down over Vietnam. Having endured torture at the "Hanoi Hilton" for six years before his release, McCain says in response to his diagnosis that he has been through worse.

"I greatly appreciate the outpouring of support -- unfortunately for my sparring partners in Congress, I'll be back soon, so stand by!" McCain posted on Twitter on Thursday (July 20). That same day, McCain's daughter Megan issued a statement, speaking to her father's tough-as-nails history: "Cancer may afflict him in many ways: but it will not make him surrender. Nothing ever has," she posted on Instagram.

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