You might not have heard of Liane Moriarty, but you probably will know about Big Little Lies - Moriarty's most famous book, which was turned into a hit TV series starring Reese Witherspoon and Nicole Kidman last year.

Now promoting her eighth work Nine Perfect Strangers, the Australian author says she wouldn't even have taken up writing if it hadn't been for her sister.

"Sibling rivalry made me start writing," she tells BBC News.

"My sister, Jaclyn Moriarty, had her first novel accepted for publication at the same time she was doing her PhD at Cambridge.

"We both wanted to be writers when we were little and I was so envious of her that that's what drove me to write my first novel.

"I'm very grateful to her for my inspiration. I don't think I would have written it - it gave me that push to finish it. It is my dream job!"

Both sisters have ended up as successful authors, with Jaclyn known for her novels aimed at children and teenagers.

Liane's stories are decidedly more grown-up, and her new book follows nine people who enrol on a 10-day wellness course at a country retreat in Australia.

The group couldn't be more different - they include a dysfunctional family of three, a young married couple and a romance novelist in her 50s (who is not based on 51-year-old Moriarty).

'We're obsessed with weight'
The group all expect to improve their health, but end up going through an experience they never expected, thanks to the vision of resort boss Masha.

"We're obsessed with wellness, it's just the latest trend so it was fun to explore," the author explains. "It is something I believe in but at the same time I like to make fun of it.

"I just know that most people going to a health resort are thinking about losing weight and I remember speaking to a friend and her memory was everyone jumping on the scales each day.

"As a society we are obsessed with weight loss and it seemed to work with a character whose husband had left her, she would think that weight loss would be the answer - she thought that it would change the way she saw herself."

Moriarty says the importance of highlighting the wellness obsession was to show "we go too far with it and believe it will answer all our problems - it's become the new religion".

While her book has only just hit the shelves, it's already had its film rights snapped up by a familiar face - Nicole Kidman.

Kidman and Witherspoon are both producers on Big Little Lies, as well as the stars.

"It's very exciting," Moriarty says. "She [Kidman] will play the role of Masha and I think she will be so good at showing her narcissism and insecurities.

"Nicole is so good at showing two things simultaneously without saying a single word - just through an expression, so she will be fantastic."

It makes sense for Kidman to get involved in adapting another of Moriarty's novels after the success of Big Little Lies, which was Moriarty's sixth novel.

The TV show, which tells the story of three mothers with children in nursery school who get caught up in a murder mystery, has been a huge hit with audiences and critics.

The first series won eight Primetime Emmys, including outstanding limited series and best actress for Kidman.

It also picked up four Golden Globes and was named as one of Time Magazine's top television shows of 2017.

Moriarty's previous novel, The Husband's Secret, is also being adapted into a film starring Blake Lively, but she insists this turn of events was never her intention.

"As I'm writing a book I never want to think, 'It will be a film'. For me the end goal is still the book so the film adaptations are a perk of the business.

"Getting to visit the [Big Little Lies] set was very exciting for me but I don't want to see myself as in the business of making films."

So when it was announced by HBO in December 2017 that Big Little Lies would be renewed for a second season, fans wondered what would happen. Moriarty hadn't written a sequel.

She ended up writing a 50,000 word novella for the series, but certainly won't be making a habit of getting involved in writing screenplays in the future.

"I did write a story for the second series, because there's not a [second book], which was a lot of fun to do," she says.

"I never plan, so I never want to rewrite something I've already written because I know what is going to happen.

"It gives me no pleasure to think of adapting one of my projects."

From BBC .