Ferguson announced the news, posting a video message to fans, dressed in period costume and teasing the book's premise, which is based on the life of her great-great-aunt Lady Margaret Montagu Douglas Scott.

Already a prolific author of children's books, biographies about Queen Victoria and two memoirs, Ferguson is dipping her Montegrappa writing pen into the world of historical fiction with the book. Set to debut in on August 3, 2021, Her Heart for a Compass will be published by romantic fiction leader Mills & Boon in the United Kingdom and William Morrow in the United States, both HarperCollins.

"History is in my blood," Ferguson says. "We all grow up listening to family stories and many people start to dig deeper after the death of a parent, suddenly realising there are unanswered questions, things they wished they had asked their parents and now can't. It inspired me to look back and see how my ancestors' lives shaped mine and that of my parents."

She continues, "The Royal Family's history is well documented, especially by Queen Victoria and her diaries. This helped me to build a framework to weave a story around Lady Margaret, an ancestor who shares my middle name, and about whom little is known."

Ferguson co-wrote the novel, set in Victorian England, with frequent collaborator and mentor Marguerite Kaye. In fictionalising her ancestor's story, the duchess interweaves real-life figures and historical events alongside fictional characters and, for its backdrop, traverses the halls of Queen Victoria's court to 1870s New York, with the country houses of Scotland and Ireland in between.

"I wanted to imagine what it would have been like to live in Victorian times and used discoveries from my research into both my parents' history to build a journey which soon took on a life of its own," she says. "It was an engrossing and exciting experience - a journey which comes from my heart."

HarperCollins also published Julia Quinn's Bridgerton novels, which have recently taken the world by storm thanks to Netflix's top-ranked original series adaptation, which is produced by Shonda Rhimes' Shondaland.

"Oh my goodness me, I am so, so proud of that! I've always loved Shonda Rhimes' and Betsy Beers' shows. I'm a great Shondaland supporter," Ferguson says of working with the literary team behind the hit show for her own novel.

"It's a happy coincidence that I started this book 15 years ago and it happens to be coming out after Bridgerton. I love tea, love wearing headbands, and love history - and these are three things everyone has gone mad about recently."

Of the series itself, she adds: "I adored it and have actually watched it twice. The costumes are beautiful. It seems to have come out at the right time to offer people a bit of escapism from this dreadful pandemic and this diabolical war we are in against a virus. Bridgerton has been able to open up a lot of color in people's hearts and it took people on a journey."

The author also sees some comparisons between Bridgerton's heroine and her own leading lady.

"I hope that Lady Margaret and her journey will also offer people some escapism from these dark times we are in and provide a lesson that whatever life throws at you, you should, never give up," she explains. "I suppose that is quite similar to Daphne; Lady Margaret keeps persevering."

Ferguson is similarly optimistic about the crossover potential for her novel, saying that she'd love to partner with Amazon Studios on a screen adaptation.

It would not be Ferguson's first foray into Hollywood. The duchess previously produced 2009's The Young Victoria alongside Graham King, Martin Scorsese and Tim Headington. The film, directed by Jean Marc Vallee and starring Emily Blunt and Rupert Friend, was nominated for three Academy Awards (netting a win for costume designer Sandy Powell) and two BAFTA's.

"It also took me 15 years to get [that] film to the screen," she recalls. "It was the greatest honor ever to be nominated for a Golden Globe, then to have won the Oscar for best costume."

The Duchess also drew inspiration from her own life; mother of Princesses Beatrice and Eugenie, Ferguson married into royalty in 1986 with a show-stopping wedding to Prince Andrew of York. (The pair divorced in 1996, with Andrew resigning from royal duties last year in relation to his association with convicted sex offender Jeffrey Epstein.)

Explaining why she feels audiences' interest in stories about royalty, nobility and romance are hard to satisfy, Ferguson says, "It's all about the fairytale. It's a dream for everybody to get their handsome prince. I'm very lucky to have been part of a real-life story like that, and to be part of it still. It's a great honour."