A month before her bestselling, Women's Prize-winning novel Hamnet was published in 2020, the premise for Maggie O'Farrell's next book appeared before her in a proverbial flash of inspiration.

Waiting in the car for her daughter to finish a playdate, she took the opportunity to reacquaint herself with Robert Browning's dramatic monologue "My Last Duchess". Intrigued, she googled the renaissance painting that inspired it: a portrait of 15-year-old Lucrezia de'Medici, third daughter of the Duke of Florence, Cosimo de'Medici, and his Spanish wife Eleonora.

Attributed to Angelo Bronzino, it is the only portrait of Lucrezia known to exist and was commissioned by her parents shortly before she left Florence to start her married life in Ferrara. She died less than a year later in 1561.

"There is something very unsettling about her picture, because she looks really frightened," O'Farrell tells me over Zoom from her home in Edinburgh, which she shares with her husband, the writer Will Sutcliffe, and their three children.

"Her eyes look very apprehensive and she looks like she wants to tell you something.

"As soon as I saw it I knew I had my next novel."

That story forms the basis of O'Farrell's ninth novel, The Marriage Portrait, which engages with the enduring speculation that Lucrezia was murdered by her husband Alfonso, the Duke of Ferrara.

The marriage portrait at the centre of the novel is O'Farrell's own creation, but it encapsulates the tensions at the heart of the story. Commissioned by Alfonso to capture what he imagines as the majesty of his young wife, it instead immortalises her restricted role as an ornament to be paraded at court.

In normal times, O'Farrell would conduct extensive research at the start of the writing process, but lockdown put travelling to Italy out of the question. She instead had to content herself with reading histories of the period, and also enlisted the assistance of art historians at the universities of Edinburgh and St Andrews.

But O'Farrell has also had a love of Italy since she first visited on a school trip at the age of 17. Eighteen years ago, she lived in Lucca, a beautiful walled town in the Tuscan countryside. She learnt Italian while she was writing the novel in order to gain an appreciation for the musicality of the language (although Lucrezia and her family would have spoken in dialect), but is thankful she could call on experts to help her understand texts from the period.

Throughout her research, O'Farrell came to understand there was "a complicated dual narrative to the renaissance" in which beauty - epitomised by the work of artists such as Botticelli, which adorned the walls of the Medici residence - was matched by the brutality of the ruling class.

An undercurrent of ruthlessness is evident in the dynamics of the Medici family. As Cosimo and Eleonora wrote to each other often, the historical record paints a rich portrait of the family's domestic life.

"There are all kinds of details about how many smocks Eleonora needs to order and who is going to inherit which dress and so-and-so is growing out of his shoes," O'Farrell says, laughing.

"I mean, it's familiar to anyone who lives with children. But actually Lucrezia barely makes a mention ... there is a little bit about her not concentrating in her lessons and day-dreaming, so I just got this sense of a sightly under-looked and under-loved daughter, in a way.

"I found the absence of affection for her and the way that she is barely mentioned very chilling."

In this respect, Lucrezia bears some similarity to the titular character of O'Farrell's fourth novel, The Vanishing Act of Esme Lennox, who is incarcerated in an Edinburgh asylum by her family in the 1930s because she desires further education over marriage. The gothic overtones of that novel are also well-suited to Lucrezia's story.

"To be honest I didn't really have to dial up the gothic aspect of her story at all - it's all there," she says.

While it is not known for certain if Alfonso killed his wife, O'Farrell certainly believes him capable of it. At the outset, she was "leaning toward trying to be generous to him" because as "a ruler, he is a victim of the system as much as Lucrezia is a sense. He will have been brought up and expected to behave in certain ways."

But after reading about his more sinister accomplishments - such as ordering his sister's lover to be murdered in front of her, a detail that makes it into the novel - she revised both her view of him and the manuscript.

Lucrezia's perilous home life resonates with our current period of reckoning with gender-based violence. O'Farrell is aghast at the fact that the home remains the most dangerous place for women all over the world.

While she stresses she has not experienced domestic violence herself, she has glimpsed firsthand what some men are capable of. In her 2017 memoir, I Am I Am I Am, she discloses that at the age of 18, while walking alone on a remote mountainside, she escaped the clutches of a killer who subsequently went on to rape and murder another young woman.

"Death brushed past me on that path," she wrote of that experience, "so close that I could feel its touch, but it seized that other girl and thrust her under."

Lucrezia, too, can sense the physical presence of death close by: "It was dark, this thing, and gelatinous, with an uncertain, shifting outline."

She visited Italy in September 2021 as COVID-19 restrictions were lifted. By that stage, she had completed the manuscript, and was apprehensive about uncovering new information that might demand a rewrite.

Fortunately, this did not happen, but O'Farrell found herself unexpectedly moved when she visited Lucrezia's final resting place at a monastery in Ferrara.

After assuaging the nuns' fears about COVID-19, O'Farrell was able to gain access but caused further commotion when she asked to see Lucrezia's tomb, which, the nuns informed her, nobody had ever asked to see before. They even double-checked whether O'Farrell meant Lucrezia Borgias, who is buried in the same place and whose name remains more recognisable than that of her Medici counterpart.

The experience brought home to O'Farrell the horror of Lucrezia "dying alone among these people who she didn't really know," which "just broke my heart all over again." She left flowers by the grave.

Upon completing the novel, O'Farrell mourned the loss of Lucrezia's presence in her own daily life, realising she had come to regard her almost as one of her own children, to whom she is similar in age. At the time of this interview in June, she was still surrounded by mementoes of Lucrezia she had pinned on her wall during the writing process and could not bring herself to take down.

O'Farrell remains an admirer of Browning's monologue. But although the poem is "brilliant", Lucrezia is silent in it.

"So I just thought I would like to bring her out from behind that curtain and tell her own story."