Prince Charles shows off proud grandpa credentials as he puts unseen family photo on display

His birthday exhibition styles him as “Prince and Patron”, a connoisseur whose childhood playing among the treasures of the palace led him to become a lifelong benefactor of the arts.

The Prince of Wales, who helped curate the Buckingham Palace exhibition in honour of his 70th birthday, has added one other important title to that list: proud grandpa.

The Prince has loaned his favourite art works, trinkets and family photographs to the show to help create a glimpse of life in his home.

Among them is a never-before-seen photograph of his cradling his firstborn grandson, Prince George, with his eldest son the Duke of Cambridge by his side.

The three future kings, rarely captured together in a photograph released to the public, look relaxed, with a baby George fast asleep in his grandfather’s arm.

The Prince of Wales and Duke both have open-necked shirts, in a casual family photograph likely taken at Clarence House or Kensington Palace in 2013.

Prince George, who turns five next week, leans into the Prince’s elbow, as the Duke, who would have been settling into life as a new father, sits protectively behind them both.

It is the first time such a candid family photograph of the three heirs together has been shown to the public.

The picture is one of a handful of images framed and put onto desks in the exhibition, along with personal ornaments and flowers in a design aimed at recreating the feel of the Prince’s own homes.

They include a photograph of the wedding of Prince Harry and Meghan Markle, the Duchess of Cornwall dressed in red, and the Prince with his arm around his younger son in 2012 after “Captain Wales” passed his helicopter pilot training.

They join more than 100 pieces from the Prince’s private collection, the Royal Collection and work by up-and-coming artists for the exhibition, which marks his 70th birthday year.

Mounted without labels, the show instead relies on an audio commentary explaining how the small, densely-hung room was inspired by Zoffany’s Tribuna of the Uffizi.

The artwork is arranged on the walls of an octagonal room with tables filled with books by the Prince, vases and other decorative objects, while above are hung rows of paintings and other artworks, some with a tapestry as a backdrop.

The Prince and Duchess of Cornwall have been in to admire the finished show before it opened to the public. The Queen has not visited, and has already made the journey to Scotland for her summer trip to Balmoral.

Vanessa Remington, senior curator of paintings at the Royal Collection Trust, said: "It's a departure because it is not a standard museum display and the works aren't shown in isolation, they're shown in profusion very, very densely. "

(Tables) are dressed with a range of objects and those are intended to show or give a flavour of the interiors of the Prince of Wales's own residences because this is a very personal show."

Speaking about one of the highlights of the exhibition, Napoleon Bonaparte's red felt hooded cloak, the Prince said: "Since, as a child, I first caught sight of this cloak in the Grand Vestibule at Windsor, I have been fascinated by the sheer magic of the colour, the dashing pattern of the lining and the enthralling story of Napoleon himself which it conjures up.

"It is said to have been worn by the Emperor during his Egyptian campaign and was taken from his carriage after the Battle of Waterloo 15 years later."

He also tell visitors via audio guide: "I am very fond of the two preparatory oil sketches of my sons which I acquired from the artist, Nicky Philipps, in 2009.

"They were painted for a double portrait that now hangs in the National Portrait Gallery. Both are dressed in the regimental uniform of the Household Cavalry - the Blues and Royals - and are particularly good likenesses."

The summer opening of Buckingham Palace, which includes the Prince & Patron exhibition, opens on Saturday and runs until September 30.