Article: Beyoncé is believed to have first started a relationship with Jay Z after a collaboration on "'03 Bonnie & Clyde", which appeared on his seventh album The Blueprint 2: The Gift & The Curse (2002). Beyoncé appeared as Jay Z's girlfriend in the music video for the song, which would further fuel speculation of their relationship. On April 4, 2008, Beyoncé and Jay Z were married without publicity. As of April 2014, the couple have sold a combined 300 million records together. The couple are known for their private relationship, although they have appeared to become more relaxed in recent years. Beyoncé suffered a miscarriage in 2010 or 2011, describing it as "the saddest thing" she had ever endured. She returned to the studio and wrote music in order to cope with the loss. In April 2011, Beyoncé and Jay Z traveled to Paris in order to shoot the album cover for her 4, and unexpectedly became pregnant in Paris.

Question: What did Beyoncé describe as the saddest thing in her life?
miscarriage