THE connection had been rumoured but never proved. The royal family has hidden credentials that make its members appropriate leaders of Britain's multicultural society. It has black and mixed-raced royal ancestors who have never been publicly acknowledged.

An American genealogist has established that Queen Charlotte, the wife of George III, was directly descended from the illegitimate son of an African mistress in the Portuguese royal house.

Charlotte, then a 17-year-old German princess, arrived in England in September, 1761, and won public affection for her loyalty and devotion to the king even during his descent into madness. She bore him 15 children during a long and mainly happy marriage, but did not have the face of a classic European beauty.

Mario Valdes, a professional genealogist from Boston, Massachusetts, said: "People in the court noted her wide nose. Her personal physician, Baron Stockmar, said in his autobiography that she had a 'true mulatto (mixed race) face'.

"Her African ancestry was certainly detectable and she wouldn't have looked as Helen Mirren depicted her in the film The Madness of King George."

Valdes has traced Charlotte's ancestry to the fifth king of Portugal, Afonso III, who had an illegitimate son with his Moorish mistress, Madalena Gil, in 1249. A small gene pool created by royal inbreeding perpetuated the physical African characteristics through the generations, he says.

"Many of the state portraits of Queen Charlotte demonstrate quite clearly her mixed-race ancestry," he said.

"Although she is chronologically distant from Afonso III and his mistress, there is a surprising genealogical proximity between the two women and six lines of descent can be traced between them. What also contributed to the perceptibility of her African heritage was the highly inbred pattern of princely German marriage alliances."

Last week one of Afonso III's Portuguese descendants confirmed the connection. Duarte Nuno Souso Chichorro Marcao, 63, who lives in Lisbon and has spent years studying royal ancestry, said he was a distant cousin of the Queen.

Gil was the daughter of Madrem, the Moorish king of the Algarve capital, and met Afonso after he conquered the city, he said. "Their son, Martin Afonso de Sousa Chicorro, later married into the Portuguese aristocracy and I have traced his descendants to the British royal family."

The colour of Gil and her son would have been of little consequence in Portugal at the time, as interracial marriages were tolerated and even encouraged. Their descendants later married into the German royal family.

David Williamson of Debrett's, the peerage guide, said there had long been rumours of Queen Charlotte's link with a black branch of the Portuguese royal family, but he had not been aware of the research showing a direct link.

"There may have been a link because there is a lot of Moorish blood in the Portuguese royal family and it has diffused over the rest of Europe," he said.

The royal family's black ancestry has been welcomed by race relations activists. Valerie Mason-John, who has written a play about a black royal throw back titled Brown Girl in the Ring, said: "Most people are not aware that the royal family has this black heritage. It is not only fascinating but many people would want to know just how diverse their background is because they are seen by many as the model family.

"The fact that there are black people in the royal family just shows how we are all interconnected. It means that they are a family that reflect both us and our heritage. The problem is that in the past there was a reluctance to acknowledge this heritage."

Valdes has not been the first person to try to show an African link with the British royal family. In the 1950s the author Ian Moncreiffe published Blood Royal, which claimed a link between the Queen and Zaid, the Moorish wife of Alfonso VI of Castille. "The international pool of blood royal has always been so intermingled that ultimately it tends to become one everywhere," he wrote.

A more recent African connection is that of Prince Philip's aunt, Nadja, who married George Mountbatten in 1916. Nadja was the great-granddaughter of the Russian poet Alexander Pushkin, who had black ancestry.

Pushkin's great-grandfather was Ibrahim Petrovich Ganni bal, an Ethiopian who was given to Peter the Great as a gift. Gannibal was well treated and was sent to France for an education in civil and military engineering. After his return to Russia he was given the rank of general.

In 1868, Pushkin's daughter Natalie married Prince Nicholas of Nassau and her daughter Sophia married the Grand Duke Mikhail. In turn, their daughter Nadja married the 2nd Marquess of Milford Haven and helped to look after Philip, her nephew, after his parents had been expelled from Greece.