Throughout her life, Princess Diana was a groundbreaking public figure who often defied Royal protocol, and her popularity stemmed, in part, from her ability to imbue the haughty and distant Windsor family with a populist humanity not really seen before she married Prince Charles.

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She continues to buck the conventional norms expected of a princess even now, 21 years after her untimely death, in the form of a super dirty joke birthday card she sent her accountant, Anthony Burrows, in the mid-'90s.

The card recently resurfaced as part of a lot that is up for sale at Julien’s Auctions, as part of their "Icons & Idols: Hollywood" sale.

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Inside the card, under the punchline, the Princess of Wales hand wrote a message for Burrows, commemorating his special day, alongside her valuable signature.

A spokesperson for Julien’s Auctions told The Huffington Post that the card is expected to fetch around $800 to $1,200 and that the auction house is selling the card for a client who obtained it from Diana's accountant himself.

The "Icons & Idols: Hollywood" sale at Julien’s Auctions runs Nov. 16-17.

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