Dilys Derwent was a healer at St Mungo's (1722-1741) and a "celebrated" Headmistress at Hogwarts (1741-1768).

Derwent had long silver ringlets. Her portrait hangs not only in Dumbledore's Office along with the portraits of previous headmasters/mistresses, but also in St Mungo's main admitting area. As she can travel between her two portraits, she was able to keep Dumbledore apprised on Arthur Weasley's condition after he was attacked by a snake in 1995.

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