With a short, tidy haircut, big blue eyes and wearing a sailor outfit, this never-seen-before picture of the Duke of Edinburgh, aged six, is at the heart of a new exhibition at Sandringham House.

The exhibition, called Prince Philip and The Sea,is being held in the ballroom to mark his 90th birthday in June.

Helen Walch, public enterprise manager at Sandringham House, said the picture – recently discovered in a family home in France – was an 'exciting addition' to the exhibition and she was delighted to put it up on display for the public to see.

She said Prince Philip had stayed at the family's home for a short holiday around 1927 and gave the picture as a gift when he left.

The picture and other items from the duke's private collection will be on show on Saturday when Sandringham House opens its doors for the first time this year.

Some of the other exhibition items include paintings, models, letters and other pictures he collected before and after his marriage to the Queen.

'Many of these items have never been put on display before,' Mrs Walch added. The unveiling of this rare picture comes just days before the duke's grandson, Prince William, ties the knot with Kate Middleton at Westminster Abbey.

It is hoped the exhibition will help people further explore the duke's life-long passion for the sea with a display of paintings of all the ships he ever served on or commanded.

There are also quirky certificates dotted around the exhibition that commemorate Prince Philip's first crossings of the Equator and the Arctic Circle and pictures of the Pacific painted by him while onboard the Royal Yacht Britannia.

Prince Philip's naval career started when he joined the Royal Navy as a cadet in 1939 and then joined the battleship HMS Ramillies in Colombo as a midshipman in 1940 and spent the following six months in the Indian Ocean.

In January 1941 he joined the battleship HMS Valiant in Alexandria and he was mentioned in despatches for his service during the Battle of Cape Matapan.

He was later appointed to the destroyer HMS Wallace based at Rosyth for convoy escort duties on the east coast.

He was promoted to Lieutenant on 16 July 1942 and in October he was appointed First Lieutenant (second in command) of Wallace at the unusually early age of 21.

He was then appointed as First Lieutenant of the new Fleet Destroyer HMS Whelp, which was present in Tokyo Bay when the Japanese signed the surrender. After instructing in the Petty Officers' School and attending the Naval Staff College at Greenwich, he was appointed First Lieutenant of HMS Chequers in 1949. He was promoted to Lieutenant-Commander in 1950 and then appointed in command of the Frigate HMS Magpie.

In 1952 he was promoted to Commander, but his naval career came to an end on the death of his father-in-law, King George VI.

Although the duke's naval career ended there, he remains to this day closely connected to, and actively interested in, every branch of service life.

In 1952, he was appointed Admiral of the Sea Cadet Corps, Colonel-in-Chief of the Army Cadet Force and Air Commodore-in-Chief of the Air Training Corps. The following year he was promoted to Admiral of the Fleet and appointed Field Marshal and Marshal of the Royal Air Force.

He is also Captain-General of the Royal Marines and Colonel-in-Chief, or Colonel, of a number of British and overseas regiments.

The house, gardens and museum will open daily from Saturday until October 30 except from between July 23 and 31, when they will be closed. Sandringham House opens at 11am. To view the house, museum and gardens costs �11 per adult, �5.50 per child and a family ticket of two adults and three children is �27.50.