A friend of Prince Charles and David Cameron.

But there's a giveaway in the surname.

Descended from the famous dynasty, author Simon Sebag Montefiore's ancestry couldn't be less English.

His paternal side are Sephardim who originated in Spain and moved to Morocco and Italy, while his mother's family came to Britain via Ireland in the early 20th century from Lithuania.

Simon's great-great uncle was the famous banker Sir Moses Montefiore and he is related to actress Gwyneth Paltrow through his mother.

"Being Jewish means everything to me," Simon said.

In fact, it means so much that, on falling in love with the author Santa Palmer-Tomkinson, he insisted that she convert to Judaism.

Simon's wife comes from a well-established English family and Santa's sister is the socialite Tara Palmer-Tomkinson.

They were married at the Liberal Jewish Synagogue in St John's Wood, London, in 1998 - and the guests included Prince Charles and Camilla Parker Bowles.

He said: "It was important to me that Santa converted. We live in Kensington and have a very English life, but we do the Friday night dinners and the festivals.

"Santa's family were wonderful about her converting to Judaism - they have embraced it and are wonderful about it.

"I think they would have preferred Santa to marry a non-Jewish boy in an Anglican church and my parents would have preferred me to have married a Jewish girl, but both families have been supportive."

The father of two girls, Sasha and Lily, it is Simon's fascination with Russian history which has marked his work.

Educated at Harrow and Gonville and Caius, Cambridge, where he read history, he had a major interest in all things Russian.

Simon, 45, explained: "The family aspect had, I think, something to do with it, what with my mother's family coming from that part of the world."

The Soviet Union had collapsed shortly after he graduated and he set about doing what he had always wanted to do - touring the broken empire.

Simon visited Tbilisi, Samarkand, Baku and even Grozny, the capital of the war-ravaged Chechnya.

He wrote a book about Catherine the Great and her lover Potemkin. "It had never been written before, a biography of Catherine and Potemkin - it had to be done".

It was shortlisted for the Samuel Johnson, Duff Cooper, and Marsh Biography prizes.

Simon recalled: "Russia fascinated me so much and still does."

Thanks to the success of the book, Russian government officials at the formerly ultra-secretive Kremlin opened their archives especially for Simon to work on his next tome, Stalin: The Court of the Red Tsar.

Hailed as a masterpiece, Simon again went travelling, to Russia and the former Soviet states to investigate the man - and dictator - behind the myth.

"He was one of the tyrannical figures of the 20th century, a sinister but brilliant character," he explained.

It was followed by Young Stalin, from which he had found unpublished material, mostly from Stalin's birthplace of Georgia.

It won the Costa Biography Award, the LA Times Book Prize for Biography, Le Grand Prix de la Biographie Politique and the Kreisky Prize for Political Literature.

And, after Miramax Films and Ruby Films bought the rights, the tale is heading for the big screen.

Simon, ever the perfectionist, is to be the executive producer, so will be able to keep a close eye on the production and filming.

His next book is perhaps one whose subject is closest to his heart.

Jerusalem: The Biography is appropriate, seeing as though the Sebag Montefiores' family motto is Yerushalayim.

It took him three to four years to research and write.

Simon said: "I've been visiting Jerusalem all my life.

"As a historian and writer it is the ultimate subject and a paramount one, too.

"I have always wanted to write a book on Jerusalem and its people, buildings, families, its dreams and illusions.

"It is how Jerusalem developed, and as a Jew, I regarded it as the holiest Jewish city. It is the place where our hearts are.

"But as a historian, I know that it is also an extremely important place for Christians and Muslims, too."

For that reason, Simon insists that the book does not have a pro-Zionist slant, nor is it a history of Zionism in Jerusalem.

He added: "There was no point writing a Zionist history of Jerusalem.

"I had to be totally objective and the book is as much about Islam and Christianity as it is about Judaism.

It is an epic history of 3,000 years, from King David and Barack Obama, from the birth of Judaism, Christianity and Islam via Jews, Persians, Greeks, Romans, Arabs, Crusaders, Ottomans and the British all the way to the Israel-Palestinian conflict.

And it will be published in Hebrew and Arabic as well.

Simon admitted that he tries to create a new way of writing in each of his books - and that he writes for himself and not the public.

"Benjamin Disraeli used to say. 'If you want to read something then write it yourself'," he explained.

Jerusalem: The Biography is published by Weidenfeld and Nicolson, priced £25.