Beyoncé:

Beyoncé embarked on The Mrs. Carter Show World Tour on April 15 in Belgrade, Serbia; the tour included 132 dates that ran through to March 2014. It became the most successful tour of her career and one of the most-successful tours of all time. In May, Beyoncé's cover of Amy Winehouse's "Back to Black" with André 3000 on The Great Gatsby soundtrack was released. She was also honorary chair of the 2013 Met Gala. Beyoncé voiced Queen Tara in the 3D CGI animated film, Epic, released by 20th Century Fox on May 24, and recorded an original song for the film, "Rise Up", co-written with Sia.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When did the tour begin?
April 15