In the later part of his life, George suffered from recurrent, and eventually permanent, mental illness. Although it has since been suggested that he suffered from the genetic blood disease porphyria, the cause of his illness is not certain. After a final relapse in 1810, a regency was established, and George's eldest son, George, Prince of Wales, ruled as Prince Regent. On George III's death, the Prince Regent succeeded his father as George IV.