But the revelation was also met with its fair share of suspicion, many suggesting Lee never wanted any more of her writing to be published, especially in her lifetime.
It was reported that although Go Set a Watchman is set 20 years later, Lee wrote it before Mockingbird, submitting the draft to a publisher in 1957.
Reports said her agent persuaded her at the time to redraft the work and that is when she came back with the American classic we all know.
Celebrated New Zealand author Jenny Pattrick said if this was true, the new book was something to be questioned.
"I imagine, from what I've read, it's a little bit controversial in some ways - that it's not a new novel but an earlier draft of To Kill a Mockingbird.
"If it was me I probably wouldn't do such a thing and I wonder whether she's been prevailed upon by people who want to make money out of it."
Pattrick, an acclaimed historical novelist who has written some of New Zealand's biggest-selling novels, said she thought an author in their full capacity of mind would not want an earlier draft of what they have finally decided going out.
"Well I wouldn't if it were me."
The first reviews of the book in US and British newspapers over the weekend suggested the biggest shock to readers would be changes to the iconic character Atticus Finch, a hero of sorts in Mockingbird who was now portrayed as a racist bigot.
Pattrick said this was not an issue for her if it was an earlier manuscript.
"It's perfectly all right for somebody to change a character ... that's perfectly legitimate and a proper way that a writer works."
She said she was sure To Kill a Mockingbird would still be regarded as a "standalone classic".
Pattrick was not planning on rushing out to buy the new book however.
"If I heard from friends that it was wonderful I might borrow their book ..."
The manager of Time Out Bookstore in Auckland, Jenna Todd, said a lot of people had already pre-ordered the novel.
She said it had created a lot of over-the-counter discussion at the Mt Eden store over the past couple of months.
"People seem to be very concerned whether it's going to be as good as To Kill a Mockingbird, but it seems like they are willing to buy the book to find out."
Meanwhile Unity Books in Wellington is also expecting a flurry of customers when it opens it doors at 9am today. Its international buyer Courtney Smith said they have also had many pre-orders.
