Kate Middleton
Kate MiddletonReuters

Pippa Middleton's recent engagement to James Matthews has reportedly caused a strain between Pippa and her sister Kate Middleton. Reportedly, the Duchess of Cambridge does not approve of James' young brother Spencer, who is a reality television star.

"[Kate] is horrified about Spencer being Pippa's brother-in-law," a source told Life & Style. "Spencer has slept his way around London and left a lengthy trail of angry women in his wake," a different insider revealed. "Kate's concerned. The last thing she wants is for William's family to turn against her because of Spencer's actions."

Spencer is a former star of "Made In Chelsea" and the British version of ABC's hit dating reality show "The Bachelor." He is known for his womanizing ways and he once told a girlfriend on the show that it was hard to respect her when she allowed him to cheat. He also revealed intimate details of his sex life in a 2014 tell-all memoir titled "Confessions of a Chelsea Boy." In it, he claimed to have slept with at least 1,000 women, and describes his experience engaging in a sixsome with some "nifty Canadian girls."

As for the Middleton sisters' alleged feud, last month, yet another report claimed that Pippa was tired of Kate being judgmental about her future in-laws, and that she was considering banning Kate from her wedding party. "After years of private drama, clashing views about courting attention and fresh concerns about a wild brother-in-law-to-be, Pippa doesn't want Kate in her wedding party," a source told InTouch Weekly. "She's fed up with Kate's judgmental attitude, and doesn't want her to be a bridesmaid unless she starts to chill out."

James popped the question to his 32-year-old girlfriend amid the scenery of England's beautiful Lake District last month. Pippa and James are expected to walk down the aisle next year. Details about the wedding are yet to be released.