Kate celebrated her twenty-fifth birthday in 2007. Although she was already in a relationship with Prince William at that time, she did not spend the day with him as he was away on military duty. Instead, the Duchess of Cambridge spent the day with her sister, Pippa. 

Catherine was once again left to celebrate her birthday alone in 2008, and, once again, it was her sister who spent the most time with her. The Middleton family went out for dinner in Chelsea, London to celebrate Kate's birthday before Kate and Pippa partied the night away at Kitts Club in Sloane Square. 

The Cambridges finally got to spend Kate's birthday together in 2009! Kate turned twenty-seven and William whisked her away to Balmoral estate in Scotland to celebrate. 

Kate's twenty-ninth birthday was a low-key affair for her, but not for her friends Harry Aubrey-Fletcher and Sarah Louise Stourton, who got married on Kate's birthday. The Duchess of Cambridge attended their wedding on her big day. 

Kate Keeps Turning 30 Simple

When Kate hit the big three-oh in 2012 she kept it simple. It was her first birthday as a member of the Royal Family and so she celebrated with close friends and family at Kensington Palace. 

The Duchess of Cambridge celebrated her 31st birthday at the Royal Albert Hall, watching a Cirque du Soleil show with her parents, sister and brother. 

In 2014, Catherine celebrated her first birthday as a mother and she spent it taking it easy at Anmer Hall in Norfolk, before joining her parents and siblings in Mustique a few weeks later for a well-deserved holiday. 

As a mother, the Duchess of Cambridge could not go out on the tiles any more, and so spent her 33rd, 34th and 35th birthdays quietly at home with her family in Norfolk.

Many have speculated that she will be celebrating quietly at home this evening with her family, just like she did last year when she turned thirty-six. We wish the Duchess of Cambridge all the best for the next year!