“I started a systematic genealogical search,” said Valdes, which is how he traced her ancestry back to the mixed-race branch of the Portuguese royal family.

Charlotte, who was born May 19, 1744, was the youngest daughter of Duke Carl Ludwig Friedrich of Mecklenburg-Strelitz and Princess Elisabeth Albertine of Saxe-Hildburghausen. She was a 17-year-old German princess when she traveled to England to wed King George III, who later went to war with his American colonies and lost rather badly. His mother most likely chose Charlotte to be his bride.

“Back in London, the king’s enthusiasm mounted daily,” wrote Janice Hadlow in the book, “A Royal Experiment: The Private Life of King George III.” “He had acquired a portrait of Charlotte and was said to be mighty fond of it, but won’t let any mortal look at it.”

King George III ordered that gowns be made and waiting for his new bride when she arrived in London.

He met Charlotte for the first time on their wedding day, Sept. 8, 1761.

“Introduced to the king, Charlotte ‘threw herself at his feet, he raised her up, embraced her and led her through the garden up the steps into the palace,’ ” Hadlow wrote. “Some later reminiscences asserted that at the moment of their meeting, the king had been shocked by Charlotte’s appearance.”

In a portrait painted by Sir Allan Ramsay, Queen Charlotte’s hair is piled high in curly ringlets. Her neck is long and her skin appears to be café-au-lait.

Ramsay, Valdes said, was an abolitionist married to the niece of Lord Mansfield, the judge who ruled in 1772 that slavery should be abolished in the British Empire. And Ramsay was uncle by marriage to Dido Elizabeth Lindsay, the black grandniece of Lord Mansfield. Dido’s life story was recently recounted in the movie “Belle.”

In 1999, the London Sunday Times published an article with the headline: “REVEALED: THE QUEEN’S BLACK ANCESTORS.”

“The connection had been rumoured but never proved,” the Times wrote. “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.”

After the Times story, the Boston Globe hailed Valdes’s research as ground-breaking. Charlotte, who died in 1818, passed on her mixed-race heritage to her granddaughter, Queen Victoria, and to Britain’s present-day monarch, Queen Elizabeth II.

Some scholars in England dismissed the evidence as weak — and besides the point.

“It really is so remote,” the late David Williamson, former co-editor of Debrett’s Peerage, the guide to Britain’s barons, dukes and duchesses, marquises and other titled people, told the Globe. “In any case, all European royal families somewhere are linked to the kings of Castile. There is a lot of Moorish blood in the Portuguese royal family and it has diffused over the rest of Europe. The question is, who cares?”

A Buckingham Palace spokesman did not deny Queen Charlotte’s African ancestry. Spokesman David Buck told the Globe: “This has been rumored for years and years. It is a matter of history, and frankly, we’ve got far more important things to talk about.”

Valdes said that in the current racial climate, the genealogy is important to history. “In reaction to the horrors of what happened in Charlottesville, which is named after this queen,” Valdes said, “her ancestry is very relevant.”