Former US Vice-President Joe Biden has offered comfort and advice to Meghan McCain over the health of her father, US Republican Senator John McCain, during a TV talk show.
Mr Biden’s son died of the same type of brain cancer afflicting Mr McCain.
A tearful Ms McCain, who co-hosts ABC’s programme The View, asked Mr Biden for his advice on how to deal with the disease.
Mr McCain was diagnosed in the summer with glioblastoma.
It is an aggressive type of brain cancer.
“Your son Beau had the same cancer that my father was diagnosed with six months ago,” Ms McCain said.
“I think about Beau almost every day and I was told that it doesn’t get easier but that you cultivate the tools to work with this and live with this.
“I know you and your family have been through tragedy I couldn’t conceive of.”
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Mr Biden said there was hope and that breakthroughs in the treatment of the disease were happening all the time.
He said Mr McCain was one of his best friends, and that “if anybody can make it, your dad [can]”.
“Her dad goes after me, hammer and tong. We’re like two brothers who were somehow raised by different fathers or something, because of our points of view.”
But he added: “I know if I picked up the phone tonight and called John McCain, he’d get on a plane and come, and I would for him, too.”
He said the key was to “maintain hope”.
The show of support elicited a number of reactions on Twitter, including people saluting the cross-partisan aspect of the encounter.
Mr Biden published a memoir last month about his son, who died of the disease in 2015.
Mr McCain’s tumour was discovered during a surgery to remove a blood clot from above his left eye in July.
A Vietnam veteran, Mr McCain, 81, spent more than five years as a prisoner of war.
The six-term senator and 2008 Republican presidential candidate underwent surgery at a clinic in Phoenix, in the state of Arizona in July.