According to Heat magazine, the couple had initially planned to spend Christmas together with Rob's family.
However, the couple's plans have now changed due to Rob's family's strained relationship with his girlfriend.
A source told Heat: "The family were smiling at Kristen and looking totally at ease on the red carpet, [during the Twilight: Breaking Dawn — Part 2 premiere] but back at the family home over the following weekend things were more difficult."
"They had a meal on Thanksgiving [22 November], and it was nerve-wracking for Kristen. She felt very uncomfortable and Rob's sisters couldn't be completely welcoming."
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Kristen Stewart and Robert Pattinson of course had a very public break up earlier this year after it was revealed that Kristen had cheated on him with 'Snow White and The Huntsman' director Rupert Saunders.
Rob eventually took Kristen back but it looks like his family is having a harder time forgiving his Twilight co-star than he is.
"It won't go back to normal straight away, even if Rob has decided to try again," the source added.
Kristen will not be spending Xmas with Rob, neither will Taylor. Copyright: [rex]
And it seems that Rob's mum has been instrumental in the actor's change in plans.
The source explained: "Rob's mum wanted him to spend Christmas with them in London and, before their trip to the UK, that had been his and Kristen's plan. From London, they were going to fly to Mexico for New Year, but that's all changed now.
"Rob's family made it clear that they really want to see him over Christmas and, after the intense promotional tour for Twilight, Rob liked the idea of spending time alone with his family."