Kate Middleton reportedly attended a “racy” and wild 50th birthday party with Prince William for her sister Pippa Middleton’s husband, James Matthews.

The big bash took place last Saturday at Matthews and Pippa’s grand home in their “sleepy” Berkshire village in England, according to the Daily Mail, which claimed that the gathering began in the afternoon and ran through the predawn hours of the following day.

The outlet reported that the soirée’s theme was “racy,” a probable wordplay and nod to the birthday boy’s career as a professional racing driver.

James, the heir to the Scottish feudal title of Laird of Glen Affric, later co-founded investment advisory firm Eden Rock Capital Management, for which he now serves as chief executive.

The billionaire married Pippa, 42 — whose backside famously made headlines at William and Kate’s April 2011 wedding — in May 2017. They now share three kids.

In addition to the Prince and Princess of Wales, both 43, other party guests reportedly included fellow retired racer Christian Horner and his wife, former Spice Girls member Geri Halliwell, as well as Matthews’ brother, Spencer Matthews, and his wife, Vogue Williams.

The event caused quite the uproar in the neighborhood, according to the Daily Mail, as neighbors blasted the couple for their “entitled” and “inconsiderate” behavior.

The celebration reportedly began with an elaborate Supermarine Spitfire fighter aircraft display over the pair’s 145-acre estate, leaving locals “concerned” that the loud sounds of the engines would bother their dogs.

The outlet reported that the “boisterous” fête with “booming” music “disturbed” neighbors until 1:30 a.m.

“It’s common courtesy and respect,” one of them told the Daily Mail. “There are a lot of very nice people who have a lot of money, but this is about entitlement. I’m a night owl and I do like parties, but I’m also aware of others.”

The neighbor argued that the duo “could easily have had a silent disco.”

Another local scoffed at “people with money,” saying, “I thought this might happen when Pippa moved in.”