Camilla was hosting a shooting party at her Scottish home over the following weekend, which meant she didn't have time to attend the wedding in Windsor, which was on a Friday, and get back for her guests.
A source told The Telegraph at the time: “The truth is that Camilla has a house party for a few friends.
“They are arriving on Friday and will be there over the weekend.
“The date of the wedding was known eight months ago so it’s strange Camilla organised her house party this weekend.”
Other excuses were mooted at the time, including the fact that Camilla undertook two engagements involving school-age children.
Royal commentator Victoria Arbiter tweeted at the time: “Turns out Camilla is carrying out two engagements with a number of children on Friday 12th, Eugenie’s wedding day.
“This stuff is not as easy to reschedule as you might think.”
However, a rift between Camilla and Eugenie's mum, Sarah Ferguson was also highlighted as a possible reason for her non-attendance.
The women reportedly have a complicated relationship as a result of being treated differently by the Royal Family.
Whilst the exact date of Beatrice and Edoardo's royal wedding is yet to be announced, it's not known who will be in attendance on their special day.
And while some say Camilla's rift with Fergie will mean she's shunned, others point out that as Beatrice is set to become a stepmother to Edo's child, the pair have shared similarities.
When she marries Edoardo Mapelli Mozzi next year, Bea will become the second royal stepmother in history, Camilla being the first.
Edo has one son, a two-year-old named Wolfie, who is rumoured to be his best man on the big day.