Dunk and Egg is a series of novellas written by George R. R. Martin, set in the same world as his as-yet-unfinished fantasy series A Song of Ice and Fire. Three stories have been published in the series so far (originally in anthologies, but they were later published together as a separate book):
The Hedge Knight (1998)
The Sworn Sword (2003)
The Mystery Knight (2010)
Martin has discussed other planned installments (with as many as 12 possible, though he has given various numbers in interviews), but has said he will not publish any before his long-awaited novel The Winds of Winter is complete.
The answers in this question will resolve independently based on how many stories in the series are published in Martin's lifetime (including the 3 already published). They can published in any form (e.g. anthologies, standalone novellas, a novel with multiple new stories), and official stories that have a co-author count, as long as the story is published (not just announced) while Martin is alive.