Former President Joe Biden’s prostate cancer has spread to other parts of his body and is causing him pain, even as he continues to speak out on public issues, his son Hunter Biden said in an interview.

In a wide-ranging interview with the CBS News partner BBC News late on Friday, Hunter Biden grew emotional as he discussed his father’s condition, describing it as very sad to watch.

“The cancer has spread, metastasized into his bones and further,” he said. “It’s very painful and it’s very debilitating in many respects.”

Joe Biden, 83, was the oldest man to serve as U.S. president and his age was a source of concern for much of his four years in office. He and his White House advisers have faced intense criticism for allegedly concealing the extent of his problems, especially after he was forced to abandon his bid for reelection after a disastrous debate with his eventual successor, President Trump.

The former president revealed his cancer diagnosis in May of last year, less than four months after he left the White House.

At the time, his office said that his cancer was diagnosed with a Gleason score of 9, which placed him in Grade Group 5, the most severe category.

Last September, the former president also underwent surgery for skin cancer in a procedure that involves cutting away thin layers of skin until only cancer-free tissue remains in the treated area. And last October, he underwent a round of radiation therapy for his prostate cancer, his office said.

In an interview with CBS News in May, former first lady Jill Biden said it was a shock when the family learned of the diagnosis.

“Honestly, I can remember getting the diagnosis, and it was just shocking,” she said.

She also indicated that the cancer was not discovered while he was serving in the White House.

“Well, you know the doctors said that, according to the American Urological Association, that men over 70 don’t need a PSA, a blood test, anymore because it’s a slow-growing cancer … I do feel we had amazing care in the White House, but somehow that was missed,” she said at the time.

Hunter Biden said the diagnosis had been tough on the family.

“It’s really sad to watch,” Hunter Biden said. “The only thing that I’d say about my dad, about his health right now, is I wish he would complain more, because it’s not good.”

But Hunter Biden said his father remains “out there,” speaking publicly about the issues that are important to him.

“He’s still doing his thing,” he said. “He so believes in this country.”

The former president will publish a memoir, “Promise Me, America,” after the midterm elections.