Princess Diana should have been on holiday in Milan when she died in a limo crash, a friend has revealed.
Fashion designer Lana Marks was a close pal of Diana's following the breakdown of her marriage.
And the two had arranged to stay in Italy together on the week of August 31, 1997.
But Lana told how she is haunted by the fact she cancelled their four-day trip at the last minute because her father suffered a fatal heart attack in South Africa.
Instead, Diana jetted off to France to be with new lover Dodi al-Fayed before their fateful crash in a Paris tunnel.
Lana, 63, told The Sun: "It was a terrible time.
"I was supposed to be on vacation with Diana in Milan right then."
Fashion designer Lana Marks
Mohamed Al-Fayed in St Tropez ten days ago
"We were going to go to Lake Como before flying back.
"I felt bad because she was at a loose end.
"I still feel the pain of it all. I constantly think, 'What if she'd been with me?'
"All that might not have happened."
Diana and Dodi during their holiday together in St Tropez in August 1997
Mohamed insists Diana found love with Dodi
It comes as the world prepares to mark the 20th anniversary of Diana's death on Thursday.
Dodi's father Mohamed al-Fayed has said the Princess had found the "safe haven" she needed in her troubled life before the pair died.
The ex-Harrods owner said she "trusted" his son who wanted to protect her and sons William and Harry.
He spoke as a letter he wrote eight years after the couple's death emerged, claiming the truth would "one day come out" about their "murder" in a Paris car crash.
Diana and Dodi in St Tropez
Mirror reports the tragedy
Mr Al-Fayed, 88, told the Sunday Mirror he would mark the anniversary on Thursday surrounded by his family.
He said: "It is a particularly difficult time for my family and I. The reality is we suffer grief every day of our lives.
"Princess Diana trusted my son and he became a shoulder to lean on at a troubled time in her life.
"Dodi wanted to be a safe haven for her and her boys. Our hearts go out to her sons. They lost a devoted mother and a wonderful human being."