When did St. Dymphna die?

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Catholic AnswerThe legend of St. Dymphna follows the same course as other stories about a King who decides to marry his own daughter. In this particular case, she refused, and the King himself cut off her head. But it is just a legend, and there is no corroborative evidence that she ever existed nor that she is St. Damhnat of Ireland. Note, St. Dymphna definitely existed and we have her relics, but the stories about her cannot be substantiated. Short answer? She was beheaded by her father, the King in the 7th century. The complete story of St. Dymphna can be found at the second link below: