July 19, 2016 11:42 AM EDT

This weekend, Prince William and Kate Middleton will welcome a new member to the family — but this time, it’s not another royal baby. Instead, it’s an uncle to their children.

On Saturday, Middleton’s sister Pippa and fiancé James Matthews will tie the knot in a private ceremony at St Mark’s Church in Englefield, Berkshire. Prince Harry will attend, as will Prince George, Princess Charlotte, and their parents. (The two youngest royals will play the all-important roles of pageboy and bridesmaid).

The church event will be followed up by a party in the backyard of the Middleton’s home in Bucklebury, NBC News reports. While the wedding is expected to be lavish, few details have been publicly confirmed. The guest list is being kept under wraps, although sources speculate that Prince Harry’s girlfriend Meghan Markle will attend the post-wedding reception, alongside celebrities like Roger Federer and Middleton’s brother, a reality TV star.

The groom is a hedge funder who runs Eden Rock Capital Management. Middleton and Matthews confirmed their engagement in July 2016. The two first dated in 2012 before splitting, although they reconnected in 2015.

Looks like William and Kate are pleased with the prospect of adding Matthews to the royal clan: “The Duke and Duchess of Cambridge are absolutely delighted with the news,” a Kensington Palace spokesperson said in a statement when they were first engaged last summer.

So who is Matthews? Educated at Eton, where both Princes also spent their formative years, the 41-year-old financier is known to be social and sporty like Pippa (even joining her for a 47-mile swim-run event and ski marathon last year). His family owns the luxe Eden Rock Hotel in St. Barth’s, and his brother Spencer was recently the star of Made in Chelsea, a popular British reality TV show.

Matthews proposed to Middleton, 33, during a weekend away in the Lake District, BBC reports, after asking her father for his daughter’s hand in marriage.

“They make a wonderful couple and we wish them every happiness together,” Michael Middleton stated in a release, saying that he and his wife were “absolutely thrilled.”

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Write to Raisa Bruner at raisa.bruner@time.com.

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