- Queen Elizabeth II celebrated her Diamond Jubilee in 2012
- Monarch's 60th anniversary on throne marked with a series of exhibitions
- Jubilee year rounded off with show of official portraits at Windsor Castle
- Works by Andy Warhol, Cecil Beaton, Lucian Freud and Annie Leibovitz featured
Four portraits of Queen Elizabeth II by pop artist Andy Warhol have gone on display at her home, Windsor Castle, for the first time as part of an exhibition of official images of the monarch marking the end of her Diamond Jubilee year.
Warhol's series of sparkling "diamond-dusted" portraits of the Queen was acquired earlier this year to mark the Diamond Jubilee.
Royal Librarian Jane Roberts told CNN they were the "most iconic" images in the exhibition, "The Queen: Portraits of a Monarch," which features pictures, paintings and sculptures by some of the world's best-known artists and photographers.
Warhol, who once claimed he wanted to be "as famous as the Queen of England," used a 10-year-old official portrait of Elizabeth II, by royal photographer Peter Grugeon, to create the four screenprints for his "Reigning Queens" series in 1985.
"What Warhol did was he grabbed a pre-existing image of the Queen and wiped it clean, so what you're left with is the outline, with the tiara," Roberts told CNN. "Then he played around with colors, and lighting, and 'diamond dust' [cut glass], really treating the likeness as an icon."
Queen Elizabeth's global significance -- as head of the Commonwealth -- is hinted at by the number of works by international photographers and artists in the exhibition: American Annie Leibovitz, Canadian Yousuf Karsh, Italian Pietro Annigoni and Czech Franta Belsky, among others.
So which, of the millions of pictures of the monarch, will be the one which is remembered long after her reign, the defining image of Queen Elizabeth II, who Roberts says is "probably the most photographed person in the world"? With so many to choose from, she says it is hard to be sure.
"I suspect in this age of photography, that it will be a photograph," said Roberts. "Probably one of the incredibly glamorous photographs taken by Cecil Beaton.
"But having said that, it could be one of the photographs taken very early in her reign, between the accession and the coronation, by Dorothy Wilding, because they were then reproduced on coinage and stamps, again and again."
"Or it could be the Warhol. Who knows?"