She wrote: “Like all couples there were moments when the effort of adjusting led to rows and disagreements and, in the summer of 1994, they came precariously close to parting.”
“Edward became what one friend described as ‘unnerved’ by the speed which the affair was developing.
“But if Edward was wracked by indecision (a not-uncommon problem amongst male members of his family) Sophie remained coolly determined," Ingrid said in her biography.
“She [Sophie] was not prepared to let the relationship flounder," wrote Ingrid.
“When rumours of the rift became public she dismissed them as ‘rubbish’.
“She was being elastic with the truth, but it did give her the breathing space she needed to get her relationship back on track again."
By the end of 1994, everything was back on track for the couple.
Sophie married Edward at St George’s Chapel on June 19, 1999.
They now have two children, Lady Louise Windsor, 15, and James, Viscount Severn, 11, who is the youngest grandchild of Queen Elizabeth.