Camilla's potential appearance caused the duchess to be branded as "inappropriate."
Nicoll said, “There was a furore when it was reported that the Duchess would be attending. Camilla herself had had misgivings and wanted to stay away, but Charles had insisted she be there.”
Rosa Monckton, one of Princess Diana's closest friends, told the Mail on Sunday: “I know such services should be an occasion for forgiveness, but I can’t help feeling Camilla’s attendance is deeply inappropriate."
The criticism from the public is said to have left Camilla “tearful”, even though William and Harry had invited their stepmother.
The debate on whether Camilla should attend even caused a rift in her marriage to Charles, Ms Nicholls also claimed..
She said: “Camilla found herself under terrible pressure, and she and Charles argued on a daily basis over whether she should attend."
Eventually, the Queen stepped in and gave Camilla her “blessing” to stay away from the event.
Camilla issued a personal statement at the time saying: “On reflection I believe my attendance could divert attention from the purpose of the occasion, which is to focus on the life and service of Diana.”