Harper Lee's "Go Set a Watchman" on sale.

Go Set a Watchman, Harper Lee's highly anticipated second novel, broke records at one of the world's largest publishing houses.

Lee's newly-released novel is the fastest selling book in the history of HarperCollins Publishers, the company announced Monday. More than 1.1 million copies of the book have already been sold in the U.S. and Canada. (Tweet This)