Pippa Middleton may be just one day away from her wedding to James Matthews, but her sister Kate Middleton isn't thrilled with the choice.

According to multiple sources, the Duchess is concerned about the hedge fund manager's younger brother Spencer, who has made quite a name for himself in reality television.

MUST SEE: Kate Middleton Worried Reputation Will Be Ruined After Hacker Targets Sister Pippa

“She is horrified about Spencer being Pippa’s brother-in-law,” a source told Life & Style, adding that the 35-year-old fears he’ll spill big family secrets in an effort to become more famous.

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The 27-year-old playboy's past certainly doesn't help. He claims to have bedded over 1,000 women and was kicked off I'm a Celebrity…Get Me Out of Here! for steroid addiction.

"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."

Despite her concern, Kate did help her little sister plan her big day.

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"Pippa isn’t having an over-the-top wedding. She wants her big day to focus on family," an insider told Closer Weekly.

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Pippa and James

Plus, Kensington Palace announced that Pippa's niece and nephew George, 3, and 23-month-old Charlotte will join the bridal party as a page boy and bridesmaid, respectively.

Even more excitedly, Harry is reported to be attending the reception with his new girlfriend Meghan Markle, marking their first official event as a couple.

MORE: Kate Middleton Plans Sister Pippa's Bachelorette Party in the Swiss Alps!

However, Pippa is still nervous.

"There have been a few nervous tears," a friend revealed to Life & Style. "And she hasn’t been sleeping well.

The source continued, "She’s deeply in love with James and knows all the drama will be worth it. She’s so happy to be starting the rest of her life with the man she loves."

For more on the royals, pick up the latest issue of Life & Style, on newsstands now. And scroll through the gallery below for our favorite Kate and Pippa moments!