As an unknown artist who had only recently arrived in England, Israel Zohar was shocked when he was hand-picked to paint a formal portrait of the Princess of Wales.

Now, as Prince William and wife Kate announce they are expecting their first child – a baby who would have been Diana’s first grandchild – he is doing a new, and more intimate, portrait of the people’s princess based on the sketches and photographs he took during the original sitting.

The 67-year-old, of Hornsey Lane, Highgate, now a world-renowned painter, still remembers the 28-year-old Diana as the “nicest, sweetest person”.

He said: “Many people ask me what she was like and I always thought that I could give a better answer in painting than in words. In quite a short time, I saw so many sides of her personality from glamour to loneliness and isolation.

“These contradictions fascinated me and evoked a lot of empathy and closeness. I feel as if I owe it to her to do a portrait that she would really like and recognise her true self in.

“A picture speaks better than a thousand words but a painting speaks better than a thousand pictures.”

Mr Zohar was born an only child in Kazakhstan in 1945 and travelled with his Russian Holocaust refugee parents to Israel in 1949, where he started studying art at the age of 13.

In 1989, only two years after arriving in England, he put on his first UK show at a Mayfair gallery and was spotted by an officer from the 13th/18th Royal Hussars, who wanted a portrait of their colonel-in-chief to hang in their headquarters.

“I imagined an old gentleman with a white moustache,” said Mr Zohar. “I had no idea it was Diana. It was a fluke of history.”

He worked day and night on the portrait for two months in 1990 during sittings at Kensington Palace and at his then studio in South Kensington.

Diana wore the midnight blue Victor Edelstein gown first seen when she danced with John Travolta at the White House in 1985. The dress was auctioned for �510,000 in 2011.

Now Mr Zohar wants to paint a very different portrait. Apart from the fact that it will be larger and will feature a standing Diana, he will allow it to take on its own form.

He said: “For many years, I felt that if I had known then what I know now – the tragedy of her life, the way it unfolded – I would have done a very different portrait.”

But Mr Zohar insists it is pure coincidence that he is working on the painting as William and Kate expect their first baby.

“Diana would probably have been very happy,” he said. “But also unhappy to be a grandmother so early!”