Cressida Bonas has been invited to Sandringham to join boyfriend Prince Harry at the Boxing Day shoot.
The royal's girlfriend has been invited to Queen Elizabeth's estate twice before but never by Her Majesty.
Sources say the weekend could be Harry's chance to get the Queen's seal of approval before popping the question.
Cressida, 24, is said to have accepted the invitation to the Norfork estate, however she will not spend Christmas with the Queen as it is a privilege restricted to married relations only.
The flame-haired prince, 29, has had an on/off relationship with the professional dancer, whose mother is 60s society beauty Lady Mary Gaye Curzon, since July 2012.
Cressida was due to be reunited with the Harry after his 200-mile expedition in Antarctica for the Walking for the Wounded South Pole Allied Challenge 2013.
Her brother, Jacobi Anstruther-Gough-Calthorpe, has previously warned that his "sensitive" sister may not cope well with the struggles of being a royal bride.
He said: "It's challenging, you can't deny it. It's not something that is easy for anyone, dating a royal or marrying into the family.
"On some level it is different to any other type of fame. It's an invasion of privacy, which is hard."