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Will Mr. and Mrs. Middleton ever celebrate Christmas Day with their daughter once she's a British royal?

This year, Kate Middleton and Prince William spent Christmas apart -- she with her parents in Berkshire, England, he doing helicopter search and rescue work in North Wales.

Going forward, the couple (who will wed April 29) will be part of the royal Christmas Day celebration at Sandringham -- and a palace source told Us, as per tradition, mum and dad Carole and Michael Middleton "will not be invited."

But that doesn't necessarily mean that Middleton, 28, won't get to make the yuletide gay with her family. "It may well be that part of Christmas Day next year William will be with his new family as well as his old," another source told Us recently.

Adds royal watcher Katie Nicholl: "The palace learned from Diana that alienating the family is not the right thing to do."

"William is determined for this to be the beginning of a new royal family with new ways of doing things," a source notes. "He wants his marriage to last."