As Princess of Wales , Kate is pretty much a permanent fixture at every major event in her role as one of the most senior royals. But before her 2011 wedding, tradition often dictated that before being married into the royal family , attending family ocassions such as Christmas and Easter was off the cards. In fact, Kate didn't join an official royal Christmas celebration with William and the rest of his family until December 2011 - the Christmas after her wedding when she was first Duchess of Cambridge.

However, when it came to her sister-in-law Meghan Markle several years later, she was allowed to join royal Christmas with Prince Harry - despite the pair not being married - leaving people asking why the same offer hadn't been extended to Kate. But according to a book, the late Queen did actually invite the princess to a festive event prior to her engagement to Prince William , but she turned it down. In his biography Battle of Brothers, Robert Lacey claims the monarch broke from tradition and extended her first invitation to an unregistered partner for the family's traditional Christmas lunch in 2006.

But Kate, who was 24 at the time, is reported to have declined the historic request. In his book, he writes that Kate "would go to Sandringham on Christmas Day only when she was engaged". He explains: "By 2006, the couple had been dating seriously for the best part of five years.

Yet when William invited Kate to join him that year at Sandringham for the Royal Family's traditio.