Reese Witherspoon and Harlan Coben are "obsessed" with their novel.

The 'Big Little Lies' star announced in October that she was teaming up with the 'Fool Me Once' author for her first foray into fiction, but the 63-year-old writer admitted he initially rejected the idea of a collaboration, only to embrace the project wholeheartedly when the 49-year-old actress shared her ideas with him.

Harlan told You magazine: "People often suggest collaborations, but I say, 'Respectfully, that's not for me.'

"I thought, 'How do I nicely tell Reese Witherspoon, who I love, this is a no?' But when she told me her idea, I was quickly thinking, 'OK, maybe if we move this bit here and that bit over there.'

"Now we are obsessed with this collaboration."

The pair are in contact every day and have found they work well with one another.

Harlan said: "We talk or text every day or she comes here. Reese is a wonderful storyteller and very bright.

"Also, she reads me well: when to push and when to back off. I couldn't work with many people, but I can with Reese."

The 'Stranger' author may not always be open to collaborations, but he'd be happy to work with "reading nerd" Queen Camilla - who he first met at The Queen's Reading Room Festival last June - if the right idea came along.

He said of the queen: "She is a reading nerd. The couple of times we've met she's been a delight. She's funny and interesting and she loves the book world."

Asked if he'd be open to writing a thriller with her, he added: "Well, yeah - but that would depend on the story, otherwise that's not fair to either party."

Reese previously admitted working with Harlan was a "dream" come true.

She in a statement issued through Grand Central Publishing, who will release the untitled novel in the autumn: "To say I am a fan of Harlan's body of work is a massive understatement.

"The fact that he found my idea for this thriller intriguing enough to want to partner with me on it as co-author is a dream becoming a reality.

"Scheming with Harlan on how to thrill audiences with mysterious characters and complex narrative twists and turns has already been more fun than I can describe. I can't wait for everyone to read what we have been imagining."