The last time the Duke and Duchess of Sussex spent Christmas at Sandringham was six years ago in 2018

King Charles in July 2023; Meghan, Duchess of Sussex and Prince Harry in Sept. 2021 . Photo: Andrew Milligan – WPA Pool/Getty; Gotham/GC

Prince Harry and Meghan Markle will not be joining the royal family for Christmas at Sandringham this year.

A source tells PEOPLE that the Duke and Duchess of Sussex have not received an invitation to this year’s royal Christmas gathering at Sandringham. The couple, who are expected to spend the holidays in the U.S., haven’t taken part in Christmas with the royal family since 2018, the year they married.

Harry, 40, and Meghan, 43, were also not invited to Trooping the Colour in June of this year, the annual birthday celebration for King Charles, which came a month after Harry and his father didn’t meet up when the Duke of Sussex was in the U.K. for the tenth-anniversary celebration of the Invictus Games. At the time, a spokesperson for Prince Harry attributed the missed reunion to the King’s “full schedule,” amid ongoing tensions between Harry and both his father, Charles, and his older brother, Prince William.

Prince Charles, Prince of Wales, Prince William, Duke of Cambridge and Prince Harry attend the commemorations for the 100th anniversary of the battle of Vimy Ridge on April 9, 2017 in Lille, France.Pool/Samir Hussein/WireImage

Prince William, his wife Kate Middleton, and their three children Prince George, Princess Charlotte and Prince Louis are set to spend Christmas at Sandringham, though both Buckingham Palace and Kensington Palace (where the Prince and Princess of Wales’ office is located) declined to comment on the Christmas guest list.

Catherine, Princess of Wales, Princess Charlotte of Wales, Prince George of Wales, Prince William, Prince of Wales, Prince Louis of Wales attend the Christmas Morning Service at Sandringham Church on Dec. 25, 2023 in Sandringham, Norfolk.Getty Images

The strain in both relationships has persisted for years, with one major sticking point being Harry’s ongoing battle over security, multiple sources told PEOPLE earlier this year. Those close to Harry suggested that his desire to discuss the matter with his father — particularly his belief that Charles has the power to reinstate his security, a legal fight Harry has been waging for over four years — was behind the absence of a meeting in May. A palace source tells PEOPLE that the idea that Harry’s security is in the King’s hands is “wholly incorrect.”

The King, 76, and Prince Harry met up in February, soon after Charles publicly announced his cancer diagnosis on Feb. 5. Since then, though, communication has deteriorated, with those close to Prince Harry saying the monarch no longer takes his younger son’s calls and doesn’t respond to his letters, either.

“He gets ‘unavailable right now,’ ” a friend of Harry’s told PEOPLE earlier this year. “His calls go unanswered. He has tried to reach out about the King’s health, but those calls go unanswered too.”

King Charles and Prince Harry, Duke of Sussex walk behind the coffin during the procession for the Lying-in State of Queen Elizabeth on Sept. 14, 2022 in London, England.Jeff J Mitchell – WPA Pool/Getty

For Harry’s part, he remains deeply concerned for the safety of Meghan and their children Prince Archie, 5, and Princess Lilibet, 3, and has repeatedly asked his father for help, sources told PEOPLE.

“Harry is frightened and feels the only person who can do anything about it is his father,” a royal source told PEOPLE. Another source added, “Harry is determined to protect his own family at all costs.”

Harry and Meghan stepped back as working members of the royal family in January 2020 and relocated to Montecito, California, where they remain. The couple “didn’t feel they had a choice,” a friend told PEOPLE. “The only option was to leave — for their sanity. I do think they thought if they got out of this bubble, there would be less focus on them.”

A key factor to move to California was, again, security — specifically the ability to have armed private security in the U.S., sources in their circle told PEOPLE. A source close to the situation told PEOPLE that the fact that Harry and Meghan stepped away from royal duty shouldn’t be a factor in their protection level, saying, “Working royal or not, this is the King’s son.”

Meghan Markle and Prince Harry attend Christmas Day Church service at Church of St Mary Magdalene on Dec. 25, 2017 in King’s Lynn, England. Chris Jackson/Getty Images

Soon after announcing their engagement on Nov. 27, 2017, Harry and Meghan spent their first Christmas at Sandringham together. In the 2022 Netflix docuseries Harry & Meghan, the Duchess of Sussex recalled fond memories from that Christmas, revealing she sat next to Harry’s grandfather Prince Philip at dinner.

“I remember so vividly the first Christmas at Sandringham,” she said. “Calling my mom, and she’s like, ‘How’s it going?’ And I said, ‘Oh my gosh, it’s amazing.’ ”

“It’s just like a big family like I always wanted,” Meghan continued. “And there was just this constant movement and energy and fun.”

She also revealed that she thought her interaction with the late Duke of Edinburgh “went really well”: “And I just thought it was so wonderful,” Meghan said of sitting next to Prince Philip. “And I was like, ‘Oh, we chatted, and it was so great.’ ”

Later, Prince Harry told Meghan that she “had his bad ear,” meaning that his grandfather likely couldn’t hear their entire dinnertime conversation. “I was like, ‘Oh — well, I thought it went really well,’ ” Meghan added.

Following those holiday celebrations — which broke precedent, as Harry and Meghan weren’t yet married and unmarried partners of royals had previously not been invited to Sandringham for the big day — Prince Harry told BBC Radio 4 that their 2017 Christmas was “fantastic.”

“She really enjoyed it,” he said in 2017. “The family loved having her there.”

Prince Charles, Prince of Wales, Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge, Meghan, Duchess of Sussex and Prince Harry, Duke of Sussex attend Christmas Day Church service at Church of St Mary Magdalene on the Sandringham estate on Dec. 25, 2018 in King’s Lynn, England.Samir Hussein/Samir Hussein/WireImage

After marrying in May 2018, the Duke and Duchess of Sussex once again joined the royal family for Christmas at Sandringham, and Meghan was pregnant with Prince Archie at the time. He would ultimately be born five months later, in May 2019.

In 2019, the new family of three spent Christmas privately in Canada. Just two weeks later, they announced their decision to step back as working royals — and haven’t returned to Christmas at Sandringham since.

Nearly five years after their 2020 step back from royal duty, nothing “would give [Harry] more happiness than being able to rekindle his bond with his father,” a friend told PEOPLE. “At the end of the day, you can’t undo bloodlines.”