Meghan Markle's engagement to Prince Harry has been called a "game changer," and it looks like the former actress is making history again. Markle will be joining Britain's royal family for Christmas, which is reportedly a first for a royal fiancée.

Kensington Palace says Markle will spend the holidays with Queen Elizabeth II and other senior royals at Sandringham, an estate in Norfolk, 110 miles north of London.

Royal expert Katie Nicholl told ET the invitation is unprecedented.

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"It's always been the case in the past that only married couples attend Christmas at Sandringham," Nicholl said. "She really will be a first in being a royal fiancée at Christmas dinner."

"It's a big deal because it's incredibly unusual. Yes, they are engaged, but Meghan doesn't have that all-important wedding band on her finger," she explains. "I think that she might well be the first royal fiancée to be invited to Sandringham for Christmas. The queen has really gone above and beyond and she's done that very simply to make Meghan feel welcome and to keep Harry happy."

Kate Middleton, now the Duchess of Cambridge, did not attend the royal Christmas celebrations in 2010, when she and Prince William were engaged.

"It simply wouldn't have been protocol for Kate to have gone," said Nicholl. "Yes, they were engaged, but she had always made it clear that she wanted to spend her last Christmas before she got married with her own family."

The holiday invitation is ultra exclusive, says Nicholl, and the Queen is "very strict about who is around her Christmas table."

The royals usually exchange gifts on Christmas Eve. They also attend a service at St. Mary Magadalene Church on Christmas Day before having lunch together, and sometimes take a walk in the woods.

Prince Harry and Markle announced their engagement Nov. 27. They are set to marry in May at Windsor Castle's St. George's Chapel.