According to The Express, the unprecedented invitation has never been extended to other royal in-laws - but for a practical reason.
As Harry shared in their November engagement interview, "I'd been seeing her for a period of time when I literally didn't tell anybody at all".More news: Walmart goes public with its Black Friday plans
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Meghan - who is thought to be around four months pregnant - wore the striking outfit during a walkabout in Rotorua on her last day in New Zealand with her husband.
It's also a huge gesture as not even Duchess Kate's family has been invited to the official royal Christmas function. Typically, Christmas at the Queen's country home is reportedly reserved only for family members.
She has remained respectful of the royal family and her daughter, unlike Meghan's father, Thomas Markle. "But I wouldn't be at all surprised if it wasn't the queen's idea, simply because, it's so important to make a new member and a future senior member of the royal family feel welcome, feel at home, and Christmas is the flawless time to do it". "The Queen knows that Meghan's family situation is complicated and that the easiest way for Meghan and Harry to be together and with Doria, which is what they want, is for them all to join her at Sandringham where there is plenty of space".