My impetus to write The Interview was a remark at a lunch that Bruce Chatwin had interviewed Eileen Gray in 1972 for The Sunday Times when her lacquer screen, Le Destin, sold for $64,000, the then highest price ever paid at auction for a "modern" antique.

Eileen Gray (1878-1976), the Irish designer, architect and painter, has been part of my life for the past two decades. I’ve researched her, written about her, dreamt about her and talked about her as far afield as Monaco, but I hadn’t come across that interview.

In the National Library, fruitlessly, I trawled through reels of microfiche. The Sunday Times office in London was helpful but couldn't help; Bruce Chatwin's wife, Elizabeth, said he'd done the interview, but, as far as she knew, he hadn't ever written it up.

Curious and curiouser. In the early 1970s Chatwin was the golden boy of Fleet Street; his profiles were news. The sale of the Destiny Screen had focused the international spotlight on the reclusive Gray for the second time in her life. And she was news. An interview by Chatwin about Gray was really big news.

She had first made the headlines in 1913 when the couturier and fine arts collector Jacques Doucet not only bought the screen but insisted she sign it – her only signed piece. Throughout the years of her success, it was well known that she disliked the media and her reluctance to be interviewed grew into refusal with age.

I knew Bruce had spent time with her from the letter he wrote from his Sloane Avenue address in London thanking her “for the most enjoyable Sunday afternoon I have spent in years”. What happened between them? What did they discuss? Most pertinently, why wasn’t the interview published?

Those questions were the hooks on which to hang the book I’d long wanted to write.

I had a wealth of material, with enough facts to give the story authenticity and plenty of scope for creativity. I also had two fascinating, high-profile characters; a conundrum of questions; settings in Paris, London, Wexford and the south of France; and a time span running from the late 1800s to the early 1970s.

The voice of the story was easily settled. But structure? After much to-ing and fro-ing, I settled on using interview techniques – it helped that I’d a background in journalism. And so began the process of sorting through my research – whiteboards, yellow stickies all over the office, a tape recorder and a notebook permanently glued to me. I’d intersperse Bruce’s questions and Eileen’s answers with various aspects of their lives. They had much in common.

I labelled the book BIP12 (book in progress 12). Ten of my books are published, the eleventh languishes in a drawer in the spare room.

It’s well-known that point of entry is one of the most important scenes in a novel. I open with 32-year-old Bruce Chatwin on his way to his meeting with Eileen Gray – browsing the second-hand book stalls along the banks of the Seine, turning into Saint Germain des Prés and walking along rue Bonaparte, his sweep of blond hair growing wet in the rain.

Cut to the fragile, lonely and melancholic Eileen Gray. Swathed in grey cashmere, moving around her apartment on a walking stick, grizzling about an unknown caller, taking pleasure in reliving the drawing of more than half a century ago that’s pinned to her board, and still battling her childhood anxiety of creeping dusk.

My two main characters had made their appearance. Now for the story of what happened between them on that damp November Sunday afternoon.

Eileen Gray, the youngest of five children, was born into an aristocratic Irish family living in Brownswood, Co Wexford. By all accounts she was a sad, lonely child with a habit of sleeping on a pillow outside her mother's door. When her father left home and marriage to pursue his career in painting, she poured all her love into Brownswood, but her sister's husband's "renovation" resulted in the simple Georgian mansion becoming a Victorian "monstrosity" – Eileen's description. Mother and daughter left to live at The Boltons, their London address.

Eileen refused to go the debutante route, be presented at Court or to consider marriage. Against family opposition she enrolled in the Slade College of Fine Arts, but it was her discovery of lacquer work in the Victoria & Albert Museum that marked the beginnings of her success. She took lessons in London and when she moved to live in Paris in 1907, she hired Seizo Sugawara a master lacquerer from Japan.

Bruce Chatwin's early years couldn't be more different. He was a war baby, the eldest of two sons, doted on by his mother and the variety of relatives they stayed with while his father served with the Royal Naval Reserve at Scapa Flow. In 1945, the family settled in Birmingham where Chatwin senior set up a successful law practice. Bruce attended Marlborough College where his schooldays are best remembered for his role of Mrs Candour in School for Scandal more than his academic or sporting ability.

With pull, his father got him a position as a porter in Sotheby’s auction house in London. Thanks to Bruce’s sharp visual acuity, he quickly rose through the ranks to become head of Impressionists. When he developed blurred vision it was attributed to the close analysis of artwork his job entailed. He resigned from Sotheby’s to read archaeology at Edinburgh University, winning the Wardrop Prize for most promising student, but left without taking his degree. By then he was married to heiress Elizabeth Chanler (a descendant of John Jacob Astor).

He was head hunted by the Sunday Times as adviser on art and architecture for its recently launched magazine. His natural charm, handsomeness, ability to draw out people and facility with words made him one of the most successful interviewers of the early 1970s.

Perhaps he won over Gray by asking her about the creation of Le Destin? She may have been flattered into telling him how she’d found inspiration in a small gallery on a rainy afternoon. His pertinently chosen questions and cautious comments would have broken down her resistance to talk of being one of the first women in Paris to get a driving licence, driving an ambulance during the first World War; the ballooning with Charles Rolls (of Rolls Royce fame) that led to her becoming a competent aviatrix, as well as being a painter and photographer and taking delight in working with materials such as cork, glass and plastic.

Gradually they would have discovered common ground.

Both loved men and women. Bruce first fell in love while at Marlborough when Ivry Guild, his best friend's sister, visited in a two-tone Bentley dressed like a 1920s flapper and removed from the boot chocolate cake and smoked sturgeon. But it is for his numerous same-sex relationships that he is remembered.

Eileen's great love was Marie-Louise Damien , best known as Damia, la tragedienne de la chansonne, a singer, actress and nightclub owner. They were a familiar sight driving the boulevards with Damia's pet panther sitting on the back seat. During the construction of E1027, regarded as one of the most iconic houses of the 20th century, she was in a relationship with Jean Badovici, a penniless Romanian architect, 10 years her junior who was editor of the prestigious Architecture Vivante.

Eileen and Bruce were seasoned travellers – she’d been to the Atlas mountains, crossed the United States by railway and flown the mail plane to Acapulco; he’d visited most of Europe and much of Asia and believed man to be naturally nomadic.

Both had problems with their eyes – Eileen’s eyesight deteriorated from the early 1930s; were non-conformists; creatively driven and upper class.

They must have discussed Patagonia. One of Bruce's favourite childhood mementoes was the scrap of skin from a sloth, sent from Patagonia as a wedding present to his grandmother. When she died four years later, Eileen willed him the gouache of Patagonia which hung in her workroom. In notes in Under The Sun, The Letters of Bruce Chatwin, authors Nicholas Shakespeare and Elizabeth Chatwin write that Bruce agreed to go to Patagonia for Eileen Gray, as she'd said she was too old to visit.

During the drafting, rewriting and evolution of BIP 12 to The Interview, Eileen Gray was a constant in my dreams. She still is… now that publication is imminent.

The Interview (New Island) by Patricia O'Reilly is launched on July 3rd by Christine Dwyer Hickey in Hodges Figgis, Dawson St, Dublin 2, at 6.30pm and all are welcome.