Demi Moore is a longtime friend of Eugenie's parents, Sarah Ferguson, the Duchess of York, and Prince Andrew

Well, that’s one celebrity we weren’t expecting to see!

Demi Moore made a surprise appearance at the royal wedding of Princess Eugenie and Jack Brooksbank on Friday.

Moore was seen arriving at Windsor Castle ahead of the ceremony. The actress stunned in a maroon dress with a matching fascinator.

Moore, 55, is a longtime friend of Eugenie’s parents, Sarah Ferguson, the Duchess of York, and Prince Andrew. She even attended a birthday celebration for Princess Beatrice in the past.

Eugenie and Jack will exchange vows at St. George’s Chapel — the same venue where the princess’ cousin Prince Harry wed Meghan Markle in May.

Princess Eugenie wedding
Credit: Press Association via AP Images

Around 800 guests are expected to attend the wedding ceremony and the lunch — with celebrity guests such as Kate Moss, Naomi Campbell, Ellie Goulding and Ricky Martin all in attendance.

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After the wedding ceremony, the newlyweds will also be feted by a lunch hosted by Queen Elizabeth Windsor Castle and then a black tie evening reception at Royal Lodge.

Eugenie and Jack are also extending the party for another full day with a festival-style event complete with a fairground and food stalls on Saturday.