The source also says Harry is "enormously fond of his mother-in-law", and she's been spending time at the couple's home, including two extended vacations this summer.
The Duchess of Cambridge did the same during her three pregnancies. "Unlike Kate who has the support of his family, the Queen acknowledges that Meghan has no other relatives in this country", explains a source to the media. "Normally, the protocol is pretty strict". However, they stayed not in the Royal Palace, and Anmer hall - located near the Norfolk residence of Kate and William.
Meghan knows what suits her - from expensive basics to her bateau neck Givenchy wedding dress - and it seems she is comfortable adjusting her signature style to suit her changing figure.
"Obviously Meghan's parents are in the United States, but the main reason [Meghan is invited] is clearly that it's what Harry wished", he continued. "The royal family have fully welcomed Meghan into the fold".
This year, as a married woman, Meghan will automatically be taking part in the holiday activities at Sandringham.
When it came to the fashion on her royal tour with Prince Harry, the Duchess of Sussex saved the best for last.
According to the Daily Mail report, Meghan Markle's mother Doria Ragland will be the first person to have received the invite apart from the Royals to spend the holiday there. However, they have previously attended Christmas day church services with the Queen and the rest of the family.
Doria joined her daughter at an outdoor reception at Kensington Palace in September to mark the launch of a charity cookbook to help those affected by the Grenfell Tower fire.
Helliker added that Ragland impressed the Queen with her quiet composure during Prince Harry and Markle's royal wedding.