Answer
Lassalle died on August 31, 1864, at the age of 39. He was killed in a duel with a Romanian aristocrat, Yanko von Racowitza, over a woman named Helene von Dönniges. Lassalle had been in a relationship with Dönniges, but Racowitza claimed that she was his fiancée. The duel took place in Geneva, Switzerland, and Lassalle was shot in the chest. He died a few hours later.