U.S. Senator and 2008 Republican presidential nominee John McCain has been diagnosed with Glioblastoma, an aggressive form of brain cancer, said his office.

 Glioblastoma is a particularly aggressive tumor that forms in the tissue of the brain and spinal cord, according to the American Brain Tumor Association.

The 80-year-old is known for political independence during more than three decades in the Senate .

The lawmaker and former Navy pilot, who was re-elected to a sixth Senate term in November, has been recovering at home in Arizona since undergoing surgery at the Mayo Clinic in Phoenix last Friday to remove a blood clot from above his left eye.

Tissue analysis since that procedure revealed that a brain tumor known as a glioblastoma was associated with the clot, his office said.

McCain’s doctors said he was recovering from surgery “amazingly well” and that his underlying health was excellent.

His daughter, Meghan McCain, said the family was shocked by the diagnosis but that her father was the “most confident and calm” of them all as he prepared for a new battle against cancer.

President Donald Trump said: “Senator John McCain has always been a fighter. Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family. Get well soon.”

Former Democratic President Barack Obama, who defeated McCain for the White House in 2008, also tweeted: “an American hero and one of the bravest fighters I’ve ever known. Cancer doesn’t know what it’s up against. Give it hell, John.”