Eight additional bridesmaids and page boys were also named.
Prince George and Princess Charlotte are officially part of the royal wedding.
Prince William and Kate Middleton's two eldest children have been named page boy and bridesmaid to Prince Harry and Meghan Markle for their wedding on Saturday.
The inclusion of Prince George, 4, and Princess Charlotte, 3, in the ceremony comes as no surprise. Royal expert Katie Nicholl told ET in March that Meghan, 36, was eager to meet the two youngsters and "really fell" for Harry, 33, after the introduction.
"Meghan is very dotting with children, she is very maternal and she was thrilled to meet George and Charlotte," said Nicholl, author of Harry: Life, Loss and Love. "The reason [Harry] wanted Meghan to meet Prince George and Princess Charlotte was so she could see that hopefully this would be hopefully replicated by them -- that they would go on to have children. You marry into the royal family but that doesn't mean you can't have a regular family with cute children. ...That was really important to him."
In addition to Harry's niece and nephew, Kensington Palace announced five more bridesmaids and three more page boys on Wednesday.
Meghan's best friend, Jessica Mulroney and her husband, Benedict Mulroney, will have their children, 7-year-old twins boys Brian and John and 4-year-old daughter Ivy, involved in the ceremony. The Mulroney family was spotted arriving at London's Heathrow Airport on Wednesday.
Meghan's goddaughters Remi, 6, and Rylan, 7, will also serve as bridesmaids for the big event. The two girls are the daughters of Benita Litt and Darren Litt, Meghan's close friends.
As for Harry, his godchildren, 3-year-old Florence van Custem, the daughter of Alice van Custem and Major Nicholas van Custem, and 2-year-old Zalie Warren, daughter of Zoe and Jake Warren, are too part of the royal wedding party. Both sets of parents are good friends with both Harry and William.
The groom-to-be's final page boy will be his 6-year-old godson Jasper Dyer, who is the son to Amanda Dyer and Mark Dyer M.V.O. According to Harper's Bazaar, Jasper's father is a former Welsh guards officer who looked after Harry growing up and is oftentimes seen as his second father.
Keep up with all of ET's coverage of the royal wedding as we count down to May 19.
Here's a look back at when Harry named William his best man:
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