One of those guests will be Peter Phillips, the only son of Princess Anne and her first husband, Capt. Mark Phillips. Born in 1977, Phillips, 43, is 16th in line to the throne and is the oldest grandchild of Philip and Queen Elizabeth. He is not a working royal.
Phillips will walk behind Philip's coffin in the procession, standing between Prince Harry and Prince William. The ceremonial service marks the first time that the brothers will have seen each other since Harry and wife Meghan's bombshell interview with Oprah, where the couple talked about why they left the royal family.
Phillips also walked alongside the brothers during the ceremonial procession for Queen Elizabeth, the Queen Mother, who died at 101, in 2002.
Phillips does not have a title, making him the first legitimate grandchild of a monarch to be born without a title in more than 500 years, according to the Express. His sister, Zara Tindall, also does not have a title, and their father rejected an offer for a title in 1973, when he married Princess Anne.
In a 2020 interview with Vanity Fair, Princess Anne said that she turned down offers for her children to have titles.
"I think it was probably easier for them, and I think most people would argue that there are downsides to having titles," Princess Anne said. "So I think that was probably the right thing to do."
Both Phillips and Tindall attended the prestigious Gordonstoun boarding school in Scotland. Several other members of the royal family, including Prince Philip and Prince Charles, were also students there.
Because he is not a senior or working royal, like his cousin Prince William, Phillips has developed his own career outside the royal family. He has worked for companies like Jaguar and the Royal Bank of Scotland.
The couple has two children: Savannah, 10, and Isla, 9. Savannah is the oldest great-grandchild in the royal family.
The couple divorced in 2020, writing in a statement that they had "jointly agreed to separate" after reaching "the conclusion that this was the best course of action for their two children and ongoing friendship."
The pair said at the time that they would "co-parent their children" and remain in Gloucestershire, "where they have been settled for a number of years." In recent years, Isla and Savannah have been photographed playing with second cousins Prince George and Princess Charlotte, the children of Prince William and Catherine, Duchess of Cambridge.
CORRECTION (April 21, 2021, 11:50 a.m.): An earlier version of this article misstated Peter Phillips' age. He is 43, not 42.