LONDON (Reuters) - From Andy Warhol's colourful depiction of Queen Elizabeth II to Cecil Beaton's pictures of her sister Princess Margaret, a new exhibition looks at portrait photography of Britain's royal family over the last 100 years.

"Royal Portraits: A Century of Photography", which opens at The King's Gallery in Buckingham Palace on Friday, features more than 150 photographic prints, proofs and documents from the Royal Collection and the Royal Archives, some of them never released or seen before in public.

"This exhibition charts the evolution of royal portraits photography over the past century, so from... the high society glamour of the 1920s all the way to the coronation of King Charles III in 2023," Allesandro Nasini, senior curator of photographs at the Royal Collection Trust and exhibition curator, told Reuters.

The exhibition begins with a 1923 engagement portrait of Prince Albert and Lady Elizabeth Bowes-Lyon, who later became King George VI and Queen Elizabeth, which hangs close to the 2023 official coronation portrait of King Charles.

"(They are) exactly 100 years apart. We have analogue technology one side, digital technology (on the other), monochrome, colour and a private commission and the official. I think gives the range... of the exhibition which goes from the very private to the very public, the official."

Among highlights is a colourful 1985 screenprint of Elizabeth II, who died in 2022, by Warhol, based on a portrait of the monarch and features "diamond dust", or fine particles of crushed glass.

There are wartime images of the royal family, including some by society photographer Beaton who took many portraits of the royal family over several decades.

A 40th-birthday portrait of Prince William's wife Kate, the Princess of Wales, hangs near a painting that inspired it: that of a previous Princess of Wales, Alexandra of Denmark.

The exhibition also features pictures of the royals by famous photographers including Annie Leibovitz, David Bailey and Rankin.

(Reporting by Marie-Louise Gumuchian; editing by Jonathan Oatis)