Kensington Palace confirmed Monday that George will join the bridal party as a page boy and Charlotte will be a bridesmaid in their aunt’s wedding to financier James Matthews on May 20.
The palace also announced that the service will be attended by close family and friends, including proud big sister, Princess Kate, Prince William and Prince Harry. It is not known if Harry’s girlfriend, Meghan Markle, will be in attendance.
Pippa and James will wed at St. Mark’s Church in Englefield, near the Middleton family home in Bucklebury, England. The royal family of four, along with the rest of the Middleton family, attended Christmas Day services at the church last year.
Matthews proposed to Middleton last July during a weekend getaway in England’s Lake District with a diamond sparkler thought to be worth over $250,000.
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Royal author Judy Wade previously told PEOPLE that Kate will likely not be her sister’s maid of honor as to avoid possibly stealing the spotlight on Pippa’s big day. (Pippa rose to fame as the bridesmaid-of-the-century at Will and Kate’s 2011 royal wedding.)
“If your sister is a future Queen, she is going to upstage the bride and draw attention. Kate would want to be in the background as much as possible,” Wade said.