George R.R. Martin of the A Song of Ice and Fire fame had published several short stories set in Westeros a century before the current events in his major series, all revolving around Aegon Targaryen V, who is known in his youth as Egg, and his Knight mentor Ser Duncan the Tall. So far he has published three short stories The Hedge Knight, The Sworn Sword, and The Mystery Knight, in three separate anthologies (Legends, Legends II, and Warriors, respectively). Now we will have all three in one volume.
The book will also be illustrated by Gary Gianni, who also illustrated the ASoIaF Calendar in 2014. According to Martin's LiveJournal page, "He loved the stories, he said, but he'd only do it if he could illustrate the entire book, with art on virtually every page." So there will be plenty of artwork.
Although he is not working on any new Dunk & Egg stories at the moment, he does intend to write more in the future, with enough ideas to fill about 10 more books. If you are interested in reading these but haven't yet read the main ASoIaF books, don't worry, as there isn't anything spoilery in the Dunk & Egg novellas for the ASoIaF books.
The book is set to be released on October 6 of this year, and is already available for pre-order on Amazon.