George R. R. Martin has announced via his Not A Blog that A Knight of the Seven Kingdoms will be published by Bantam on October 6th 2015.
This publication collects the three pre-existing Tales of Dunk & Egg novellas (The Hedge Knight, The Sworn Sword, and The Mystery Knight) into one tome.
The novellas follow the adventures of the hedge knight Ser Duncan the Tall and his young squire Egg. While existing in the same Westeros we all love from Game of Thrones, the stories take place roughly one hundred years before the main Ice and Fire saga, and are notably lighter in tone.
As of now, the novellas are only available as individual parts of three separate short-story collections; Legends, Legends II, and Warriors. This re-publication will make the stories much more accessible to general audiences.
According to GRRM, there will be art on “virtually every page”. Artist Gary Gianni will already be familiar to Ice and Fire fans as the man who provided art for the 2014 edition of the ASOIAF calendar. Some samples of his work from that publication can be seen below.
As for the future of Dunk and Egg, we know that GRRM has at least two more novellas planned with the working titles of The She-Wolves of Winterfell and The Village Hero.