It's been a very trying year for GOP Senator John McCain.

In early 2017, the politician underwent surgery to remove a blood clot above his left eye, but doctors found something even more alarming during the procedure: a tumor in his brain.

They concluded "that a primary brain tumor known as a glioblastoma was associated with the blood clot."

"They said that it's very serious. That the prognosis is very, very serious," McCain told 60 Minutes. "Some say three percent, some say 14 percent. You know, it's a very poor prognosis. So I just said, 'I understand. Now we're gonna do what we can, get the best doctors we can find and do the best we can.' And, at the same time, celebrate with gratitude a life well lived."

Although his prognosis was said to be very poor, McCain has been fighting hard, and his family has been there with him every step of the way. Every so often, they would release updates about the Senator's progress.

He underwent a round of chemotherapy, but it wasn't without complications. Last fall, he found himself back in the hospital after experiencing some nasty side effects from the cancer treatments.

A statement from his office later reassured the public that this was a "normal side effect of his ongoing cancer therapy." It continued, "As ever, he remains grateful to his physicians for their excellent care, and his friends and supporters for their encouragement and good wishes. Senator McCain looks forward to returning to work as soon as possible."

The Vietnam veteran and prisoner of war, who turns 82 on August 29, built up enough strength to attend his daughter Meghan McCain's wedding on November 21, 2017.

He later told People magazine that seeing his daughter walk down the aisle was a dream come true.

Earlier this year, McCain's family announced that the frail senator had been hospitalized once again for intestinal surgery at the Mayo Clinic in Phoenix. He made a full recovery shortly after, and returned to his ranch in Arizona.

Now, the McCains are sharing more information about the politician's treatment, but this time, the news is not what everyone was hoping to hear. According to the new statement, McCain has made the decision to end all of his medical treatment.

The statement reads:

Last year, Senator John McCain shared with Americans the news our family already knew: he had been diagnosed with an aggressive glioblastoma, and the prognosis was serious.

In the year since, John has surpassed expectations for his survival. But the progress of disease and the inexorable advance of age render their verdict. With his usual strength of will, he has chosen to discontinue medical treatment.

Our family is immensely grateful for the support and kindness of all his caregivers over the last year, and for the continuing outpouring of concern and affection from John's many friends and associates, and the many thousands of people who are keeping him in their prayers. God bless and thank you all.

Meghan wrote on Twitter that the "family is deeply appreciative of all the love and generosity" people have shown them over the past year. She added, "Thank you for all your continued support and prayers. We could not have made it this far without you - you've given us strength to carry on."

McCain's wife, Cindy McCain, also took to Twitter to express her love for her husband, and gratitude for their supporters. She wrote: "I love my husband with all of my heart. God bless everyone who has cared for my husband along this journey."

McCain's fellow politicians also had some words to say about the unfortunate update on Twitter.

"God bless John McCain, his family, and all who love him "” a brave man showing us once again what the words grace and grit really mean," wrote former Secretary of State John Kerry.

Republican Senate leader Mitch McConnell wrote that he was "very sad to hear this morning's update from the family of our dear friend." He added, "We are so fortunate to call him our friend and colleague. John, Cindy, and the entire McCain family are in our prayers at this incredibly difficult hour."

We're thinking of McCain and his family during this very difficult time in their lives.