Former US president Joe Biden's prostate cancer has spread to other parts of his body and is causing him pain, his son Hunter said in an interview. This was reported by infohub.kz.

In a wide-ranging interview with the BBC, Hunter Biden discussed his father's condition, saying it is 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."

Biden, 83, was the oldest man to serve as US president, and his age was a source of concern for much of his four years in office. He and his White House advisers faced intense criticism for allegedly concealing the extent of his health issues, especially after he was forced to abandon his re-election bid following a disastrous debate with his eventual successor, Donald Trump.

The former president revealed his cancer diagnosis in May of last year, less than four months after leaving the White House. Hunter Biden said the diagnosis has been tough on the family. "It's really sad to watch," he 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."

However, Biden said his father remains "out there," speaking publicly about issues important to him. "He's still doing his thing," he said. "He so believes in this country." Biden will publish a memoir, Promise Me, America, after the midterm elections.