Every year the Queen travels to Sandringham with the royal family to celebrate Christmas, and they have a number of famous traditions - from a royal Christmas dinner including turkey, shrimp and lobster, to the annual 'weigh in' after the feast.
But there's one tradition that the monarch is known to follow when it comes to who makes the guest list. While partners often attend the lavish affair, an invitation is usually only extended once the couple is married.
However, this rule was broken in 2017 when Prince Harry took his then-fiancé Meghan Markle to the Queen's estate to celebrate Christmas alongside the royals, months before their wedding in May 2018.
It seems that the same offer was on the table for Prince William and Kate Middleton in 2006, as the Queen asked the now Duchess of Cambridge if she would like to attend the festivities - but Kate turned it down and 'refused' to join William and his family, according to a new book.
Historian Robery Lacey's Battle of Brothers, which is due to be released later this month, largely details the relationship between William and Harry, but also claims that the Duchess chose not to make the trip to Norfolk.
The book, serialised by the Daily Mail, explains why Kate - then 24 years old - declined the offer despite dating the prince for five years.
Lacey, who has worked consultant on the Neflix drama, The Crown, writes: 'When William invited Kate to join him that year at Sandringham for the Royal Family's traditional Christmas lunch, she refused.'
It was the Queen's decision to invite Kate, and was an unprecedented move, 'the first time the Queen had extended such an invitation to an unregistered "girlfriend".'
Lacey continued: '[Kate] would go to Sandringham on Christmas Day only when she was engaged and had a ring to prove it.'
The Duchess made her first appearance at the royal estate in 2011, eight months after marrying William at Westminster Abbey.
