“Anne was indifferent to Diana from the very beginning," said biographer Ingrid Steward in her book Prince Edward, reports Express.co.uk.
The week of racing proved an ordeal for Diana, who wasn't a huge fan of horse racing and horses - unlike her soon-to-be sister in law.
“She treated the woman, who by marriage to her elder brother might have become her Queen, with withering disdain.
“She called her ‘a silly girl’,” Ingrid continued.
Everything came to a head shortly before Lady Diana married Prince Charles, in a fairytale royal wedding at Westminster Abbey on July 29, 1981.
Diana tried to ingratiate herself with Anne by venturing to the nursery at Windsor Castle, where the family were staying and Anne was settling her young children.
“Diana, still only a Lady, gave the Princess the benefit of a full curtsey and declared: 'Ma’am, how wonderful to see you'," Ingrid continued.
“Anne is contemptuous of pretension at the best of times.
“When she was struggling with two small children she had no time for it at all.
“She looked up at Diana – and looked straight through her.
“Diana, confronted by the searing force of Anne’s scorn, fled the room.”
Ingrid's account of Anne was backed up by royal reporter, Richard Kay, reports Express.co.uk.
“Princess Anne, she had no time for Diana.
“She didn’t like the way she went about her duty and the way she used the cameras and the media to promote herself, in her eyes.
“Anne had a much more traditional approach to monarchy and royal duty,” he said.