LONDON (AP) ¿ Richard Leigh, a writer of alternative history who unsuccessfully sued for plagiarism over themes in Dan Brown's blockbuster novel "The Da Vinci Code'', has died, his agent said Friday. He was 64.

US-born Leigh, who had lived in Britain for three decades, died in London on November 21 of causes related to a heart condition, the Jonathan Clowes Agency said.

Leigh was co-author of "The Holy Blood and The Holy Grail'', a work of speculative non-fiction that claimed Jesus Christ fathered a child with Mary Magdalene and that the bloodline continues to this day.

A best-seller on its release in 1982, the book gained new readers after Brown's thriller, which explores similar themes and has sold more than 40 million copies, was released in 2003.

Leigh and co-author Michael Baigent sued Brown's publisher Random House, claiming "The Da Vinci Code" "appropriated the architecture" of their book. A third "Holy Blood" author, Henry Lincoln, did not join the lawsuit. The authors made a striking pair during the lengthy High Court hearing — Baigent professorial in a suit and tidy gray hair, Leigh sporting a leather jacket and thick sideburns. In April 2006, High Court judge Peter Smith threw out the claim, saying the ideas in question were too general to be protected by copyright.

The prominent court case sent "Holy Blood" back up the best-seller lists, but Baigent and Leigh were left with a bill estimated at almost $6.2 million.