Hildegarde the Death-Bride

Hildegarde the Death-Bride was a fictional character featured in the 19th century book of horror stories Tales of the Dead. After George Gordon Byron read aloud from the book to the other guests at the Villa Diodati, Mary Shelley half-joked, when a loud knocking came at the door, that it might be none other than the Death-Bride herself. It was in truth Team TARDIS, come to observe the genesis of Frankenstein, who would go on to uncover something genuinely horrific in the Villa in the form of Ashad, who was quite unrelated to any fictional Death-Brides. (TV: The Haunting of Villa Diodati)

Behind the scenes
Hildegarde the Death-Bride is in fact the main spook of one of the stories in the real-life Tales of the Dead anthology, The Death-Bride by German writer Friedrich August Schulze, a German novelist who wrote under the pen name Friedrich Laun.