Merton's remarkable career began when he was a boy, besotted by Boticelli, his works in later life were clearly influenced by the Italian Renaissance.

Let's begin with the first big impression Merton made on the art world. In the mid 1940s, Merton created three portraits to be shown at the Royal Academy Summer Exhibitions. When the selection committee dismissed his triple portrait of Mrs Daphne Wall, the RA's president, Sir Alfred Munnings, fought back and threatened his public resignation if the portraits did not make the final cut.

In 1987, Merton's triple portrait of Diana, Prince of Wales, was unveiled to the world. At the time of its release, the artist gushed ''she is undoubtedly the most beautiful woman I have ever painted''

In an interview, Merton's daughter Nicola Merton-Richard, recalled when Princess Diana came to their family home in Oare, Wiltshire, to sit for the portrait which was the centre of a Royal controversy.

The painting of Diana took Merton some 1 000 hours to complete. Whether he was painting the Queen of the Princess, Merton would insist his subjects would come to his studio in his Wiltshire home.

merton3_1835426b John Merton alongside his portrait of Diana, Princess of Wales

''I remember the day Diana sat for my father in 1986 very well because she was so delightful,'' Nicola recalled.

''The lane was filled with security men but she had only one bodyguard with her. First, she and my father had lunch, then he took several pictures of her, then she sat for several hours, after which time she had had quite enough so she flung off her shoes and scampered around the garden. It was so lovely; such a girlish thing to do,'' said the artist's daughter.

merton2_1835422b John Merton's triple portrait of Diana, Princess of Wales (1987)

The portrait was hung in Cardiff City Hall until in 2005 it was temporarily removed from the wall just hours before the Prince of Wales and wife Camilla, the Duchess of Cornwall, were arriving on an official visit. The controversial decision was met with much criticism.

John Merton's portrait of the Countess of Dalkeith (1958) John Merton's portrait of the Countess of Dalkeith (1958)

However, Merton will be remembered for his talent for capturing his subjects in the most beautiful of ways. His portraits of Jane Dalkeith (now the Dowager Duchess of Buccleuch) was hailed ''the picture of the century'' by Cecil Beaton.

John Ralph 1913-2011, oil on canvas view of Iradnor Hill in Herefordshire, sweeping landscape scene with fields in the foreground, Iradnor Hill in the middle distance and with sky and clouds behind, inscribed J.R.Merton 78, mounted in a fine wooden frame with applied gilded decoration, H 75 cm W 93 cm John Ralph 1913-2011, oil on canvas view of Iradnor Hill in Herefordshire, sweeping landscape scene with fields in the foreground, Iradnor Hill in the middle distance and with sky and clouds behind, inscribed J.R.Merton 78, mounted in a fine wooden frame with applied gilded decoration, H 75 cm W 93 cm

Auctioneers Criterion's auction in Islington, London, next week, will feature this painting by John Ralph Merton. His works are an important part of British history, with examples hanging in Buckingham Palace and the National Portrait Gallery.

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