(CBS) — Pulitzer Prize-winning author Harper Lee has died.

A city hall clerk in Lee’s hometown of Monroeville, Alabama, has confirmed her death at the age of 89, according to CBS News.

Her book To Kill A Mockingbird became an American classic, selling more than 40 million copies worldwide since its publication in 1960. Lee won the Pulitzer Prize for the novel in 1961. A year later, it was made into a film starring Gregory Peck, and the movie won three Academy Awards.

The novel addressed racial injustice in the south as it followed the story of Scout, the protagonist, and her father, Atticus Finch, a lawyer who defends a falsely accused black man of rape in 1930s Alabama.

It was the only book she published until last year, when a sequel Go Set A Watchman hit store shelves.

Many fans were disappointed by a significant change to the Finch character, but were thrilled to finally hold a copy of a sequel 55 years in the making.

In Mockingbird, Finch defended Tom Robinson, a black man falsely accused of raping a white woman. In Watchman, Finch is depicted as a racist and segregationist, breaking the heart of now-grown daughter Scout.

Although set after the events of To Kill A Mockingbird, Lee actually wrote Go Set A Watchman first. After she submitted Watchman to a publisher in 1957, she was told to rewrite it with a younger Scout.

The Watchman manuscript was found in Lee’s safe deposit box. Her lawyer has hinted there might be a third book on the way.

Watchman sold more than 1.1 million copies in less than a week; publisher Harper Collins said it was the fastest-selling book in history.