George R.R. Martin knows all the signs of Boba Fett Syndrome.

Named for the minor “Star Wars” character who fans demanded to know more about, Boba Fett Syndrome is most acute for any book or film series that has reached the level of phenomenon, when minutiae becomes major. For Martin, this has meant not just the usual demands for the next “A Song of Ice and Fire” fantasy novel (don’t ask, he’s still working on it), but constant letters and emails asking for information on everything from dragons to Aegon Targaryen’s war against the Seven Kingdoms.

Martin’s new book, released this week, is “The World of Ice & Fire: The Untold History of Westeros and the Game of Thrones,” 300 pages of back story and original artwork by the some of the world’s top fantasy illustrators. He agreed to the companion volume in 2006 and expected it would take just a couple of years. Naturally, it took longer. He intended to write some brief text to accompany the drawings, but ended up setting down some 300,000 words, more than enough to make his editor’s “head explode.”

“It was bigger than I anticipated,” he said during a recent telephone interview, acknowledging that “The World of Ice & Fire” might have delayed still further the next “Ice and Fire” novel. “I start these things that I think won’t take much time and they grow and grow.”

Martin said “The World of Ice & Fire” offers material already in the “Ice and Fire” series, material he has long worked out in his mind and on paper, but had never released, and material he invented entirely for the book, such as the section dedicated to lands on the other side of the Narrow Sea. (Fans of Tyrion Lannister, be advised: Martin includes little about the character he has called his favorite. He’s saving that for future books).