Camilla reportedly has a prior engagement at a school near her Scottish home Birkhall, believed to have been arranged, before the date for the nuptials was announced.
The 71-year-old is expected to be the only senior member of the royal family to miss the ceremony at St George’s Chapel in Windsor.
A source said: “When this date was proposed, she said that regrettably she couldn’t come.
“The family understood, particularly Eugenie, and were fine about it owing to her previous commitment. Camilla didn’t want to let anyone down.”
The royal diary, which announces official engagements up to eight weeks in advance, currently does not have any entries for the Duchess of Cornwall on October 12.
Yahoo UK has asked Clarence House for comment.
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