It turns out we've been mispronouncing the name of "He Who Must Not Be Named."
Harry Potter author J.K. Rowling revealed on Twitter that the "t" in Lord Voldemort is silent, in the style of the French language, though Rowling admits she's likely the only person who pronounces it that way.
... but I'm pretty sure I'm the only person who pronounces it that way. https://t.co/HxhJ5XY5HP— J.K. Rowling (@jk_rowling) September 9, 2015
Narrator Jim Dale did pronounce Voldemort with the silent "t" in the series' audiobooks, prior to the release of the movies. It's a wonder then that Rowling didn't correct the actors on the film, considering how closely she worked with them.
Personally, I'm looking forward to Voldemort's Comedy Central late night satire series, The Voldemort Report.