Alabama-born author Harper Lee, whose book "To Kill a Mockingbird" became one of the most beloved, widely-read and best-selling novels of the 20th century, has died at the age of 89, Fox News has confirmed.

Hank Conner, Lee oldest nephew and the family spokesperson said:  “This is a sad day for our family. America and the world knew Harper Lee as one of the last century’s most beloved authors. We knew her as Nelle Harper Lee, a loving member of our family, a devoted friend to the many good people who touched her life, and a generous soul in our community and our state. We will miss her dearly.”

Lee, who won the 1961 Pulitzer Prize for fiction for "Mockingbird," published just two novels in her lifetime. She released “Go Set a Watchman” in July 2015, more than 50 years after “To Kill a Mockingbird” hit bookshelves.

Lee, who never married, did her best to stay well out of the spotlight for many years after “Mockingbird,” turning down interview requests and leading a reclusive, intensely private life in her hometown of Monroeville, Alabama.

Aside from receiving the Presidential Medal of Freedom at the White House in 2007, little was known about her later years.

Nelle Harper Lee was born in Monroeville on April 28, 1926, the youngest of four children. Her father was a lawyer and her mother's maiden name was Finch – both facts reflected in her creation of the character Atticus Finch, "Mockingbird's" lawyer-hero and moral compass.

Lee was known as a tomboy and individualist growing up. She moved to New York City in hopes of becoming a writer and after several years of mundane jobs, was given a spectacular Christmas present by her friends Broadway composer and lyricist Michael Brown and his wife, Joy.

"You have one year off from your job to write whatever you please," they said in a note accompanying a year's worth of wages.

Lee threw herself into writing "Mockingbird," which was published in July 1960. A story of racism, a trial in the South, social conscience and what Lee once called "the conflict of the human soul," it was narrated by a young girl named Scout – based on the youthful Lee.

In 1962, it was adapted into the classic movie starring Gregory Peck, who won a Best Actor Oscar for his portrayal of Atticus Finch.

Lee, who called it "one of the best translations of a book to film ever made," became close friends with Peck and his family, reportedly giving him the gift of her own father's watch.

"Mockingbird" went on to become a classic of American literature and sell more than 30 million copies in 18 languages.

In 1999 it was voted Best Novel of the Century in a Library Journal poll and in 2006 British librarians ranked it ahead of the Bible as one book "every adult should read before they die."

In July 2015, Lee released “Go Set a Watchman” after it was rediscovered. The novel is essentially a sequel to "To Kill a Mockingbird," although it was finished earlier.

"In the mid-1950s, I completed a novel called 'Go Set a Watchman,'" Lee said in a statement at the time. "…I hadn't realized it (the original book) had survived, so was surprised and delighted when my dear friend and lawyer Tonja Carter discovered it. After much thought and hesitation, I shared it with a handful of people I trust and was pleased to hear that they considered it worthy of publication. I am humbled and amazed that this will now be published after all these years."

“Go Set a Watchman” quickly because a best-selling book, selling more than 1 million copies in the first week it was released.

Lee's comments on "Mockingbird" over the years were few and far between. In 1964, she recalled her hopes for the book, saying, "I never expected any sort of success with 'Mockingbird.' I was hoping for a quick and merciful death at the hands of reviewers but, at the same time, I sort of hoped someone would like it enough to give me encouragement.

"Public encouragement. I hoped for a little...but I got rather a whole lot, and in some ways this was just about as frightening as the quick, merciful death I'd expected."

The Associated Press contributed to this report.