Prince Archie and Princess Lilibet are set to celebrate a  "special" Christmas this year as their mum, Meghan Markle, braces for a "bittersweet" moment, a source has claimed.

The Duke and Duchess of Sussex are expected to spend the festive season in Montecito, California, where they reside with their family; however, as they both are strained from their families, they'll allegedly be joined only by Meghan's mother, Doria Ragland, according to reports.

Archie and Lilibet are now old enough to fully "get it" when it comes to the festivities, as they are said to be anticipating the "special" day.

A source told OK!: "This year feels special because both children fully ‘get it' - they’ve been talking about Santa and Christmas for weeks.

"They always wait until Thanksgiving is over before putting up their tree and decorations but they will go OTT!

"The kids will have their own tree to decorate, while the main tree will be a bit more colour-coordinated! They will have lots of people over for the holidays - Doria will even move in for a bit."

They added: "Christmas is Meghan’s favourite time of year, she loves seeing everyone over for Thanksgiving, and then they are in full on countdown mode for Christmas.

"Harry is also very excited and loves seeing how excited Archie and Lilbet are getting.

"He sometimes can’t believe how lucky he is to have them."

The source added that Christmas is often a "bittersweet" moment for the couple who "wish that they could have all their families together."

They said: "They [Harry and Meghan] both really wish that they could have all their families together and have a huge Christmas but they know that will never happen.

"So they have to make new memories and traditions with their children and those close to them."