oswaldite:

_{Knight of the Laughing Tree (as Lyanna Stark) was a mystery knight who fought at the Tourney at Harrenhal. He defended the honor of  Howland Reed by challenging and defeating three knights whose squires had bullied him, demanding that they chastise the squires in order to ransom back their horses and armor. The Knight of the Laughing Tree is so-called because of the blazon on his shield, a smiling heart tree. His true identity remains unknown.}