Prince Jacaerys Velaryon, nicknamed Jace, was the firstborn son of Princess Rhaenyra Targaryen and her first husband, Laenor Velaryon. When Rhaenyra was crowned queen, she named Jacaerys as Prince of Dragonstone and heir to the Iron Throne. Jacaerys was adragonrider; his dragon was Vermax.
History
Jace was fifteen-years-old at the start of the civil war which became known as the Dance of the Dragons. He rode his dragon, Vermax, to the Eyrie, Sisterton, White Harbor and Winterfell to raise support for his mother's claim. He successfully gained the North and the Vale of Arryn for the blacks.
He took part in the Battle in the Gullet where Vermax flew too low and went crashing into the sea. It was said that Jace leapt free and clung to a piece of smoking wreckage for a few heartbeats until some crossbowmen on the nearest Myrish ship began loosing quarrels at him. The prince was struck once, and then again. Finally, one quarrel took him in the neck and he was swallowed by the sea.