The Mirror's editor Richard Wallace has paid tribute to the popular journalist, who lost his battle with cancer this morning (February 15).
"James was a true Fleet Street legend who became famous around the world as a royal reporter," he said in a statement. "His colleagues often joked that at times he appeared grander than the royals themselves - which, of course, he loved.
"Despite the severity of his illness, he never complained or went in for self-pity, but insisted he had a life well lived. Our thoughts are with his loving family who - like us all - will miss him terribly."
A Buckingham Palace spokesman commented: "Those in the Royal household who knew James were extremely sad to learn of his death."
The Sun's royal photographer Arthur Edwards tweeted: "He was a great man and a brilliant reporter."
In 1994, he published his book Diana v. Charles, which looked at the relationship between Prince Charles and Diana, Princess of Wales.
In recent years, Whitaker served as a royal commentator for ITV's This Morning and competed in the 2004 series of Celebrity Fit Club.