One of the most influential American novels of the 20th century and biggest bestsellers of all time, “To Kill a Mockingbird” was believed to be the first and only novel by Nelle Harper Lee (born April 28, 1926), until now.

On July 14, HarperCollins will release Lee’s earliest known work, “Go Set a Watchman,” featuring characters from her Pulitzer Prize-winning novel, which was published 55 years ago (July 11, 1960).

In honor of this landmark literary event, THIRTEEN’s “American Masters“ series presents a newly updated version of Emmy-winning filmmaker Mary McDonagh Murphy’s 2012 documentary “Harper Lee: Hey, Boo,” broadcast as “Harper Lee: American Masters” on Friday, July 10, 9-10:30 p.m. on PBS (both WTVI and UNC-TV). The author of “Scout, Atticus & Boo: A Celebration of To Kill a Mockingbird,” Murphy was able to read an advance copy of the new novel before updating the film and will live tweet (#HarperLeePBS) during the broadcast.

“ ‘Go Set a Watchman’ was written before ‘To Kill a Mockingbird’ and believed to be lost or destroyed. Its remarkable discovery allows readers of Lee’s beloved classic the chance to see Atticus and Scout again. How and why this happened is a mystery we unravel in the new version of the documentary,” said Murphy.

Lee once said she wanted to be South Alabama’s Jane Austen, but became an enigma when she stopped speaking to press in 1964 after her whirlwind success. “Harper Lee: American Masters” offers an unprecedented look at Lee’s life, illuminates the phenomenon behind “To Kill a Mockingbird” and the Oscar-winning 1962 film adaptation, and previews “Go Set a Watchman,” which Lee wrote in 1957.

The documentary features interviews with Lee’s friends and family – including her centenarian sister Alice (now deceased) – who share intimate recollections, anecdotes and biographical details for the first time: Lee’s rise from small-town Alabama girl to famous author, her tumultuous friendship with Truman Capote, and the origin of her most memorable characters: Atticus Finch, his daughter Scout, her friend Dill, and Boo Radley.

The film also explores the context and history of the novel’s Deep South setting and the social changes it inspired after publication and through the feature film starring Gregory Peck.

Oprah Winfrey, Rosanne Cash, Tom Brokaw, Pulitzer Prize-winners Rick Bragg, Anna Quindlen, Richard Russo, Jon Meacham and Diane McWhorter, James Patterson, Wally Lamb, Scott Turow, civil rights leader Andrew Young, and others reflect on the novel’s power, influence, popularity and the ways it has shaped their lives.