The oldest known survivor of the Holocaust's Nazi concentration camps has died. His biographer made the announcement that Leopold Engleitner, the oldest known Holocaust survivor, died at 107. Engleitner was confined between 1939 and 1943 at the Buchenwald, Ravensbrueck, and Niederhagen Nazi concentration camps.

"It's very hard for me to announce the painful news of the passing away of my best friend," Rammerstorfer, his biographer, wrote on his website.

The Mauthausen Committee, which tracks Holocaust survivors, confirmed Thursday that Leopold Engleitner died April 21.

Besides being the oldest known survivor of the camps, Engleitner is notable because his struggle was documented in the book and film "Unbroken Will".  Bernhard Rammerstorfer, the  Austrian author and producer, published a biography about him and an accompanying documentary in 1999. They were translated into English in 2004.

Engleitner was a conciencious objector and refused to renounce his faith as a Jehovah's Witness. To do so may have won him freedom, but he steadfastly refused, even though his weight plummeted to 62 pounds (28 kilograms). Eventually, he was released on the condition that he work as an indentured slave for the remainder of his life doing forced agricultural labor.

After being "released" from the camp, Engleitner then went to work on a farm in Austria, eventually going into hiding in the mountains to escape being conscripted to the German army. He was released from his farm labor sentence in 1946 by U.S. Army troops.

After the war, he carried on missionary work and held a variety of jobs. Much later in life, after his biography was released, he embarked on speaking tours in the United States and Europe, talking to students and community members about his experiences during the Holocaust. He was able to attend the U.S. premiere in November 2012 of a new documentary film about his life, also produced by  Rammerstorfer.

Engleitner did not have surviving family, but passed away peacefully in the company of Rammerstorfer and his family on April 21. He was 107.