Something he had seen or heard unhinged his mind. He lost his memory completely.
5 seconds sound clip from the Dracula: Prince of Darkness movie soundboard.
You can hear this line at 01:05:28.908 in the Blu-ray version of the movie.
Quote context
[...]
- A chance to resurrect his master.
- Admirable. Another 24 hours and she'll be as good as new.
- Ludwig would like to see you, Father.
- Come with me Mr. Kent. Ludwig should interest you.
- He was a traveler, like yourself. I found him one night near Castle Dracula.
- Something he had seen or heard unhinged his mind. He lost his memory completely.
- We brought him here, and here he has remained these past 12 years.
- Oh, he's a contented enough soul, and a brilliant craftsman.
- I seek shelter for the night.
- I'm sorry, my son, but I have orders to let no one in tonight.
[...]