Joan Collins broke this royal protocol with Kate Middleton

Joan Collins made a royal faux pas when she encountered Kate Middleton at the late Queen Elizabeth’s Platinum Jubilee Pageant in June 2022.

The soap opera star, 90, recalled the awkward yet funny moment in her recent memoir, “Behind The Shoulder Pads.”

Collins admitted that she was so nervous that she broke protocol during her meeting with the Princess of Wales, 41.

During last year’s pageant, the English actress was riding in a car down The Mall during the bash alongside supermodel Twiggy and TV presenter Prue Leith.

“Finally, we arrived outside the Royal Box, which was packed with royals and relatives of the Queen,” the “Dynasty” alum wrote.

She continued: “As we descended from the Jaguar, trying to look presentable after two hours in the freezing wind, Princess Beatrice and her husband Edoardo [Mapelli Mozzi] waved at us excitedly.”

Collins recalled that Mozzi “nudged Princess Anne, who nudged Prince Charles and Camilla, and they all waved, smiled at us, and mouthed, ‘Well done!’ Very gratifying indeed.”

Following the procession, she was filed into the green room behind the box and was able to take a beat.

“I collapsed onto a sofa and was offered a cup of tea,” Collins said.

Then SURPRISE — Middleton was in Collins’ midst.

“Suddenly, a vision appeared in a red dress. Katherine, the [then] Duchess of Cambridge, with her two young children in tow,” she went on.

“‘Hello, Joan,’ [Middleton] said sweetly, holding out her hand.” To which a surprised Collins replied back: “Hello, ma’am.”

She continued: “I gulped, forgetting to curtsy.” Middleton then introduced her daughter Princess Charlotte and son Prince Louis to the dame.

“Both little people held out their tiny hands politely for a handshake,” Collins penned.

The “Guiding Light” actress had met the duchess on more than one occasion in the past — at a reception at Buckingham Palace in 2014 and another instance in 2017 at the Royal Variety Performance show.

Louis, 5, was the star of the Platinum Jubilee at the time, with his wild antics making royal fans fall in love with him by the minute.

The little prince stole the show during the Platinum Jubilee flyover while standing next to his family on the balcony of Buckingham Palace.

He made a medley of funny faces and hilariously plugged his ears to block out the jets’ loud noise.