"Yesterday, love was such an easy game to play," Paul McCartney sang in the 1965 hit.
But after his wife Linda died of breast cancer in 1998, he spent a difficult year crying.
The former Beatle, 77, speaking to BBC Radio Scotland to promote an exhibition of photographs - taken by Linda - that has just opened in Glasgow, said: "I think I cried for about a year on and off.
"You expect to see them walk in, this person you love, because you are so used to them."
"I cried a lot. It was almost embarrassing except it seemed the only thing to do," said the pop icon who married Linda, an award-winning photographer, in 1969.
McCartney said his response to grief contrasted with that of his father.
When McCartney's mother died in 1956, also from breast cancer, he noted: "We had no idea what my mum had died of because no one talked about it."
He was 14 then.
"The worse thing about that was everyone was very stoic, everyone kept a stiff upper lip and then, one evening, you'd hear my dad crying in the next room."
"It was tragic because we'd never heard him cry. It was a quiet private kind of grief."
McCartney has happy memories of Linda, saying that living on a farm in Scotland with her and their four children brought a respite from the demands of pop stardom.
"We did what we wanted and she took pictures of it all."
McCartney, who is now married to business mogul Nancy Shevell, said Linda had a knack for making people feel relaxed in her company.
In an interview with the Guardian, he noted: "One of the things about Linda, when you talk about how people seem at ease in her photos, is that it was her lifestyle.
"We'd say: 'Let's go out of London' so I'd just drive. I'd say: 'Where do you want to go?' She'd say: 'Just anywhere.'
"After a while, you'd end up in areas you didn't know, going: 'Ooh, I'm getting a bit lost here' and she'd say: 'Great.' You were in places you'd never been, you were seeing things you hadn't intended to see, all of which was rich stuff for her photography."
He added: "I always used to joke that I ruined Linda's career. She became known as 'Paul's wife', instead of the focus being on her photography."
The exhibition, which runs till Jan 12, 2020, will help to set the record straight.