From Protector of the Grey House:
Although Vincent didn’t need to, he took a deep breath. After all these years he still felt that a deep breath was the best way to calm himself. He closed his eyes and felt as his chest rose and fell unnaturally, felt the tightness around his scar as the skin stretched. He placed his right hand over the scar and smiled. He could heal the scar but didn’t want to. It was a reminder of one of his greater moments. He had gained Joseph’s undying loyalty and the scar in the same instant.
Fifty years after Vincent’s change, Joseph had been ordered to kill him by their benefactor. According to Gautier, young Vincent was too flamboyant and public with his abilities. To weaken him they trapped Vincent in his room. After five days Joseph came to him. offered false friendship to get close, and staked him. When Joseph stumbled into him, Vincent felt the wood pierce the skin and part his muscles. Vincent did not turn to dust.