The Duke and Duchess of Cambridge have released an official portrait of Prince George to mark his 4th birthday.

Prince George Alexander Louis, who is Kate and William's eldest child and heir to the throne, was born in 2013 and turns 4 on Saturday (22 July).

The adorable close up picture captures George beaming into the camera with a wide joyful grin. The Prince is dressed casually in a blue and white striped, collarless shirt, for the official photo.

In a statement the palace said: "The Duke and Duchess are very pleased to share this lovely picture as they celebrate Prince George's fourth birthday, and would like to thank everyone for all of the kind messages they have received."

The photo was taken at Kensington Palace at the end of June by Chris Jackson, Getty Images Royal Photographer

Recalling the shoot Jackson said in a statement: "I'm thrilled and honored that the Duke and Duchess of Cambridge have chosen to release this portrait to celebrate Prince George's fourth birthday. He is such a happy little boy and certainly injects some fun into a photo shoot!"

It's the first time the royals have released an official portrait of Prince George on his birthday. Previous photos released to celebrate his birthday were taken by his mother Kate in an informal setting.

Prince George
The Duke and Duchess of Cambridge have released an official portrait of Prince George to mark his 4th birthday AFP/Getty

According to E! News a palace spokesperson said the family will be celebrating his birthday together at their home in Norfolk.

The photo was released at the end of a week-long European tour which saw William and Kate embark on a tour of Poland and Germany with their two children Prince George and Princess Charlotte.

The royal family set off on a charm offensive on behalf of the foreign office to bolster relationships with key EU countries ahead of Britain's exit from Europe.

The official tour also proffered numerous charming photo opportunities of the royal children with a sleepy Prince George emerging from the plane and later tugging at his father's arm as they faced diplomatic line ups off the plane in Warsaw and Berlin.

Photographer's also captured his delight as he was taken inside two helicopters on the tarmac at Hamburg ahead of the journey home and allowed to wear a helmet.

In September, Prince George will start at the private school Thomas's Battersea, where fees cost £17,604 a year.

The family will also be relocating from their Norfolk based home Anmer Hall and will take up residence at Kensington Palace in London.

IBTPOTY2017 Pictures of the week
19 July 2017: A shy Prince George hides his face as he arrives with his mother, father and sister at Tegel airport in Berlin Kay Nietfeld/Reuters