De Villiers was diagnosed with pancreatic cancer in May and died Thursday shortly after publishing the 200th book in his "SAS" pulp-fiction series, Britain's The Daily Telegraph reported Friday.
The SAS series, named for its spy hero's honorific title, "Son Altesse Serenissime," or "His Most Serene Highness," followed the exploits of Austrian spy contractor Malko Linge.
Though de Villiers felt he never got the recognition he deserved in his home country, he sold roughly 150 million copies of his books, and intelligence chiefs the world over praised his writing for being eerily accurate, The Daily Telegraph said.
He used real operatives as sources and wrote about international incidents that would often later come true.
In 2012 he wrote about the CIA fighting Islamist groups in post-revolutionary Libya six months before the raid that killed U.S. ambassador Christopher Stevens.
"I recommend to our analysts to read his books, because there's a lot of real information in there," one former CIA operative told The New York Times.
Just before his death, de Villiers signed a contract with Random House for five of his books to be printed in English for the first time. They are set to be released in the United States and Canada in 2014, Radio France Internationale reported.