The late beatle's teenage sweetheart, who became his secret wife for six years at the height of Beatlesmania in the 1960s, had returned home early from a holiday in Greece when she encountered her husband and Ono, dressed in bath towels, in her conservatory.
She recalls, "I was so devastated... I felt as though I didn't even exist in this situation because they were so tightly knit. It was so obvious that they'd been up all night.
"I said the most stupid thing that I've ever said and I've regretted it ever since.
"I'd come back from holiday; I'd come from Greece to Rome and planned dinner in London - I thought that was a great idea. I came back with friends, got in, saw what was going on and I said, 'Do you fancy going out? We've had breakfast in Greece and lunch in Rome, do you fancy coming out for dinner in London?'
"Yoko didn't look at me and John said, 'No thanks.'"