Kate Middleton's Regal Look at King Charles' Coronation Includes Princess Diana and Queen Elizabeth's Jewelry

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The Princess of Wales looked every bit the royal at the coronation.

Kate Middleton is looking stunning at King Charles III's coronation. The Princess of Wales stepped out for the historic event on Saturday, May 6, wearing a blue cape and silver floral headpiece as she entered Westminster Abbey alongside her husband, heir apparent Prince William, and behind the king. 

The Princess of Wales sported an Alexander McQueen design for the special occasion: an ivory silk crepe dress with silver bullion and embroidery featuring rose, thistle, daffodil, and shamrock motifs signifying the four nations. She honored her late mother-in-law, Princess Diana, by wearing the South Sea Pearl Earrings that previously belonged to the former Princess of Wales. She also paid homage to the late queen Elizabeth II by donning the George VI Festoon Necklace, a three-strand diamond necklace made in 1950 at the request of King George VI for his daughter, then-Princess Elizabeth. 

As for her floral headpiece, it is a collaboration between milliner Jess Collett and Alexander McQueen featuring silver bullion, crystal, and silver threadwork leaf embroidery. 

The couple was joined in the procession into Westminster Abbey by their two younger children, Princess Charlotte, 8, and Prince Louis, 5. Their firstborn son, Prince George -- second in line to the British throne -- became the youngest future king to have a role in a coronation when he served as a page behind his grandfather. Charlotte donned an Alexander McQueen dress, cape, and headpiece in similar style to her mother's.

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Kate is on hand for the ceremony that will formalize Charles' role as the head of the Church of England and mark the transfer of his title and powers as he's officially crowned king. He'll be crowned with the St Edward's Crown from the 17th century, which weighs nearly five pounds, has a solid gold frame and 444 stones.

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It's also a big day for Camilla Parker Bowles, who will be anointed and crowned as queen. Camilla will be the first divorcee to be crowned, and the coronation invitation that was released in April made headlines when it referred to her as Queen Camilla for the first time. Until then, she was described as queen consort.

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Also there on Saturday is Charles' younger son, Prince Harry.. He's attending the coronation solo, as his wife, Meghan Markle, is set to stay at their home in Montecito, California, with their two children -- son Archie, who turns 4 on coronation day, and 1-year-old daughter Lilibet.

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The Duke of Sussex's decision to attend the ceremony comes amid tension with his family following the December release of Netflix's Harry & Meghan, and the January release of Spare. Both the doc and Harry's memoir were critical of the royals and shared intimate details about them from the couple's perspective.

Despite Harry and Meghan's estrangement from the royals, the couple is featured in the official souvenir program celebrating the coronation, which includes a happy photo of the family -- including William, Kate and their three kids, Prince GeorgePrincess Charlotte and Prince Louis -- celebrating King Charles' 70th birthday in 2018.

When ET spoke to royal expert Eloise Parker, she weighed in on how William and Kate feel about Meghan opting out of the coronation.

"I think there's bound to be some relief from William and Kate that Meghan won't be attending the coronation simply because less emphasis is going to be on them, who's looking where, who's lip reading, what's going on between them," Parker said. "There's such a fever of interest in these relationships and the truth is we're never going to see a Real Housewives moment between these women. Everything is going to be kept firmly under wraps and I think for Kate, the fact that Meghan isn't attending, helps her keep it that way."

Although the actual anointment during the coronation ceremony is not broadcast publicly, plenty of special programming and live footage from the ceremony will be available to watch live on May 6, starting at 5 a.m. ET. Cable viewers will be able to view coverage on ABC News and Good Morning America, including the concert featuring Katy Perry and Lionel Richie on Sunday, May 7. Others can watch the coronation online on these streaming platforms.