"Do you really wish to know?" Spoilers from the books and/or games to follow!
Windhalm of Attre was the prince of Attre. A chubby youngster of 12, born in the year 1240, he was one of the young men that visited Cintra to vie for the hand of PrincessPavetta. He was chaperoned by the knight Rainfarn.
Later in 1267, now around 27 years old and a duke, he led a rebellion in Cintra against Nilfgaardian invaders, but was ultimately captured. Emhyr var Emreis, the emperor of Nilfgaard, wanted to make an example of him and ordered his public and spectacular execution.