It is a big day for King Charles today as he marks his 76th birthday – and several years ago on his landmark 70th birthday, a heartwarming photo of him surrounded by his family was released, but behind the scenes tension was brewing

His day today might be filled with the usual royal duties of public appearances and dealing with state papers – but no doubt King Charles will also carve out time to celebrate his birthday.

The monarch, who is undergoing treatment for cancer, turns 76 today and will mark the ocassion by opening several food distribution hubs as it also marks the first anniversary of the Coronation Food Project. His birthdays are usually low-key affairs but five years ago when he turned 70, Charles decided to celebrate the day by releasing several gorgeous family photos.

In them, he proudly sits beside wife Queen Camilla with his sons Prince William and Prince Harry also in the photo along with the Princess of Wales and the Duchess of Sussex. His three oldest grandchildren – Prince George, Princess Charlotte and Prince Louis – are also in the snap, although Prince Archie and Princess Lilibet missed out as the photo was taken before they were born.

But while fans loved the rare family shots, it was reportedly an “absolute nightmare” to arrange as William and Harry made very little effort in making sure the shoot happened, a book claims. In the bombshell biography Finding Freedom, authors Omid Scobie and Carolyn Durand claimed that the royal brothers “can be hot and cold with their father”.

The authors wrote: “The boys can be hot and cold with their father’ disclosed a source, who gave the example of planning the photo session for Charles’ 70th birthday, which they called ‘an absolute nightmare’. Neither William nor Harry made much of an effort to make themselves available, the source said.”

Two photos from the photoshoot were released, the first a more formal snap and the second a candid picture which shows the family laughing. However, since that day, it seems the two brothers have gone on to have very different relationships with their father.

Despite their sometimes bumpy relationship, Charles and William are now said to have a bond “built on love, affection and respect”. The pair both share a passion for tackling climate change and William publicly pledged his allegiance to his father at the Coronation last year.