Harper Lee’s Go Set a Watchman is bestselling book of 2015 in US

Harper Lee's second novel Go Set a Watchman topped the US bestseller list in 2015, selling 1.6 million copies, more than half a century after her Pulitzer-winning first book was published.

The figures were based on US print unit sales reported to Nielsen since the novel was published in July, snapped up by avid fans who for decades thought the reclusive author of To Kill a Mockingbird would never publish another word.

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Advance orders last February – made right after the book was announced – made it an instant bestseller before it was released, in fact. The novel features many of the characters of Lee’s 1960 masterpiece, which was turned into an Oscar-winning movie starring Gregory Peck.

Considered a 20th century classic that defined racial injustice in the Depression-era South of the United States, Mockingbird is standard reading in classrooms across the world.

Lee’s second published novel, which earned mixed reviews, was seemingly discovered in her safe deposit box in still-unclear circumstances.

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The 89-year-old is now confined to a nursing home, her sight and hearing deeply affected by a stroke, and has given no public interviews for years.