Nick Clegg has revealed how the decision to take his teenage son to the doctor for a "tiny bump" led to the shock diagnosis of blood cancer.
The former deputy prime minister said it was after a family holiday in northern Spain in September 2016 that his son Antonio began complaining about a lump on the top of his chest.
In an interview with the Sunday Times Magazine, Mr Clegg described the 15-year-old, who he shares with his wife Miriam Gonzalez Durantez, as an "incredibly active, physically strong boy".
"To this day, I don't know what possessed me to take him to the GP," he said. "It was those early days in September, you know, when you have to get kids ready for school.
"Miriam had to work very heavily that week, so I was at home most of the time, helping to do the preparatory things, buying clothes for the new term - and Antonio said he had this thing.
"We had an afternoon, so I thought, 'Why don't I just take him, and he'll stop going on about it'."
Mr Clegg said it was unusual for his son to complain, and that his decision to seek help was out of character - as normally he is "quite brutal" owing to the mentality of his Dutch mother who thought going to the doctors should be avoided.
The former Liberal Democrat leader said the GP was "brilliant" as "lymphoma is quite a difficult thing to diagnose".
"You could barely see it with the naked eye. But he took pretty much one look at him and said, 'That's not right'," he told the publication.
Describing the cancer as like a "huge bunch of black grapes" when viewing the x-ray, he said from then on it felt as though they they were "sailing through a storm".
Mr Clegg said: "Antonio was extraordinarily brave and resilient. I'm not sure he fully appreciated the enormity of it at the time."
He said his son is now back at school, and in September told how Antonio received treatment at University College Hospital in London - undergoing chemotherapy and taking heavy steroids.