Princess Diana Dress Auctioned Off For $1.1 Million

One auctioneer is royally out of pocket ... shelling out a record-breaking $1.1 million on an evening dress once worn by Princess Diana.

Diana famously took the Jacques Azagury-designed evening gown out for a spin in Florence, Italy, on April 23, 1985 ... and close to 4 decades later, the frock has been sold for a whopping $1,148,080.

The final figure was 11 times more than what it was expected to rake in ... having been initially listed for an estimate of $100,000 - $200,000 on Julien's Auction.

It was the top-selling item of the auction house's 4-day "Hollywood Legends" sale -- also breaking the world record for the most expensive dress worn by the late Princess sold at auction.

It's a stunning gown ... complete with celestial-print embroidery, a large bow, and on-trend shoulder pads -- and long before Kate Middleton became the queen of recycling, Princess Diana wore it again to the Vancouver Symphony Orchestra in 1986.

This dress was so influential it was also displayed at London's Kensington Palace for their Fashion Rules exhibit from July 4, 2013, to July 10, 2015.