My great-uncle Alfred Hollis was in his early 40s when he died; he was a bachelor and had never worked. According to my aunt, he was always dressed beautifully, quite beyond his means. In the only photograph I have of him, he is sporting a rakishly angled wide-brimmed hat with a feather in its band, a high, stiff collar, a waistcoat and a long jacket. He is leaning his hip elegantly against his stick and holds a cigarette in his left hand. Parkland stretches behind him. He has written on the picture: "The one and only... I took this 15 years ago."

In the winter of 1938-39, Alfred visited the south of France with his sister Amelia and her husband Albert Emery, my maternal grandparents. Amelia wrote in her diary in January 1939 that they were "nicely settled in a charming hotel on the promenade of Cap Martin... the beautiful blue sea under my window and oranges and lemons growing along the streets". She described the distractions of the resort, in particular the casinos, and her "great difficulty" in stopping "my husband in trying to break the bank". Alfred may also have enjoyed the nightlife, but his main aim must have been to improve his health, or perhaps just to die in a pleasant place. He had spent much of his adult life in Ware Park sanatorium in Hertfordshire. Nine of his siblings had died of TB, in infancy or childhood. Now he seemed likely to follow; he was already so weak that, to his great chagrin, he had to wear a leather and steel surgical corset.

I have been told different stories about his death on January 28, 1939. My mother maintained that he died in a sanatorium near Menton. My aunt, on the other hand, remembers being told that, coming down for dinner, my grandmother found her brother sitting in an armchair in the hotel lounge with a martini in his hand, a small drop of blood on his closed lips the only indication of death. Amelia and Albert stayed on to arrange the funeral and burial in the hilltop cemetery of Roquebrune, above Menton. They chose a grave plot, the lease on which, according to the usual practice in France, had to be renewed after 10 years.

WB Yeats died in Cap Martin on the same day. His family chose the same sort of plot; the two men were buried alongside each other and their graves marked by plain white marble slabs bearing just their names and dates. Family photographs show both graves strewn with wreaths and flowers and Alfred's headstone has an ornate wire frame fixed behind it, covered with more flowers. Amelia and Albert were the only mourners at Alfred's funeral on January 30 1939. According to the Paris correspondent of the Times, those at Yeats's graveside included "Mrs Yeats, Mr Dermod O'Brien, the President of the Royal Hibernian Academy of Arts, and Lady Gerald Wellesley, the poetess".

In February 1947, my grandparents again made the trip to the south of France, accompanied this time by their teenage daughters. My mother recalled her intense excitement, and the ivory-framed sunglasses and frocks bought for the trip. In one of her daily letters to my father, she described their visit to the cemetery at Roquebrune. All the graves in the part of the cemetery where Alfred was buried had disappeared. Although they went to the local officials and the priest, they couldn't find any trace of his grave and no one knew or would say what had happened to his remains.

The explanation given to my distraught grandmother was that there had been fighting around Roquebrune and that, in the confusion, all burial records had been lost. The family was determined to discover what had happened to Alfred's body. "I must say if ever my husband said he would do a thing," my grandmother wrote in her diary, "he would do it and I have never known him to let me down."

In the Times of January 6 1948, my grandfather read that Yeats's "last wish", expressed to his wife, was that his remains be returned to Ireland for reburial in Drumcliffe churchyard, County Sligo, where he had "spent his early days and where his father lived and his great-grandfather was once rector". Arrangements for the exhumation were being made, according to the Sligo corporation and its mayor, AJ Dolan. How was this possible? The Yeats family must have known that the graves had been destroyed during the war. Or did they know something my grandfather didn't? Alternatively, were the authorities trying to cover up the fact that the graves had been destroyed?

Albert wrote to Yeats's son, Michael. His letter has not survived but the reply has. It is a kind letter, and Yeats agrees with Albert that "the position with regard to the cemetery at Roquebrune would appear to be more than a little confused". He had not been to Roquebrune himself, but says that he was told that the disturbed remains were removed to an unmarked corner of the cemetery. "In the case of my father certainly, and probably also in the case of your brother-in-law, the concession given was a 10-year one, and should not therefore have expired until early next year.

But it would seem that during the war, changes occurred in the administration of Roquebrune cemetery, and conditions were for a time much disturbed - you will remember that fighting took place in and around Roquebrune... they have clearly made a mistake as regards the time for which certain of the concessions were granted. As far as the remains of my father are concerned, they have been traced and are now lying in a vault ready to be taken home as soon as transport can be arranged. But you will understand that the circumstances in this case were exceptional."

Albert was unhappy with the response. He hadn't seen any unmarked graves in the cemetery. And, more disturbing, he had read in the press that the body waiting to go to Ireland was said by a French doctor to have been encased in a steel and leather surgical corset.

The arrangements for Yeats's reburial continued. On August 20, the Times reported that in two days' time the corvette Macha would leave Cork for Dublin, and that Sean MacBride, the minister for external affairs, would join the ship on its journey to Villefranche, where the casket said to contain the poet's remains would be collected. The Macha would then return to Sligo Bay, where a state funeral was being arranged.

The Times correspondent at Marseille reported that the casket had been collected on September 6 in the presence of Sean Murphy, the Irish government's representative in Paris, M Haag, prefect of the Alpes Maritimes, and a detachment of French troops. The next report says that the remains were interred on September 17 in Drumcliffe churchyard, after first lying in state at Sligo town hall. Picture Post added that the Yeats family had wanted a quiet ceremony but the government had insisted on a state funeral with full honours.

The Times didn't mention that there was some doubt about who was buried in Drumcliffe, but my grandfather's questions were echoed in the Picture Post of October 9 1948. John Ormond Thomas, a staff journalist, had made inquiries at Roquebrune and "despite close questioning and examination of all the people who should have been able to produce conclusive proof", he was "still not convinced" of the identity of the body in the casket. Local officials at first denied that Yeats had ever been buried there, and later told him that they had discovered that the death had been entered in the register under the name "William Butler".

They wouldn't let him see the register and didn't seem to understand how important Yeats was. Thomas was also shown two different plots where Yeats was supposed to have been buried, one by the sexton, who had not been present at the exhumation, and another by the undertaker. The first plot seemed to have been reused, although it was now empty; the date on the headstone was 1946. It didn't look like the grave shown in the photographs published in the Irish Times during the war. Thomas went to look at the casket, which stood in the chapel "before a small altar that was covered with jampots that had once held flowers" with a madonna and "mildewing cherubs" looking down from the damp walls.

It was all very odd: the casket looked too new to have been in the earth for nine years, but the plaque on its lid was very tarnished. My grandfather wrote to Picture Post and received a reply from the assistant editor, EC Castle: "What you say," he wrote, "seems to justify the doubts which our staff journalist and photographer had when they started to ask questions about the grave at Roquebrune." On October 25, he heard from John Thomas, who said that the editor wanted to thank Albert for his letter and a subsequent visit he had made to their London office, but they had decided that "it would be best for us not to pursue the matter further in Picture Post, if only out of respect for the Yeats family's feelings". He enclosed an office memo:

Dr William Patrick Griffin, who is a Harley Street physician, says that he has definite proof that when the body of the Irish poet WB Yeats was brought home from abroad in 1948 and buried with great ceremony in Sligo, the coffin contained not WB Yeats but a man whom of all people the Irish thoroughly disliked. He knows the name but was unwilling to divulge it at this stage. He would like to discuss the matter, and terms, with someone. He understands that we pay generously for exclusives. I told him we would ring him.

This note is typed on unheaded paper, although an address, 530 Fulham Pal. Rd SW8, is scrawled on the bottom. Nothing more is known about Griffin's claims - my great-uncle appears to have had no connection with Ireland - but they make clear that others were aware of the doubt as to the identity of the body in Drumcliffe.

My grandfather was also told by Picture Post that his activities were threatening relations between Ireland and France. Others agreed. Hugh McNally of the Daily Express wrote to Albert, saying that he had "gone into the whole affair" and had also decided not to "publicise what had happened". The warnings must have had a great effect on my grandfather: he didn't investigate the matter any further.

Some of the confusion can perhaps be explained by a visit Yeats's last lover, Edith Shackleton, made to Roquebrune accompanied by the painter Gluck in the summer of 1947. This is what Gluck's biographer, Diana Souhami, reports: the two women, having searched in vain for Yeats's grave, questioned the local priest, Abbé Biancheri, and Pierre Reynault, director of Maison Roblot, a firm of undertakers at Menton; they also visited Roquebrune town hall.

They were told that Yeats had been buried in a "fosse commune", a pauper's grave, and that the site had long since been dug up and the bones placed in the communal ossuary. None of this tallies with either Michael Yeats's or my grandparents' account, and is belied by the photographs Albert took at the funeral. Biancheri did, however, speak to César Lottier, the official responsible for exhumations and the maintenance of graves. He then wrote to Shackleton and Gluck saying that Lottier had only a vague memory of the exhumation, but that he thought a "surgical truss circled with thin strips of steel" had encased the body believed to be Yeats's.

The women hurriedly consulted the artist Edmund Dulac, a close friend of Yeats's, who wrote to Biancheri on June 27 1947 imploring him not to let the matter go any further. The priest was asked to reveal nothing, no matter who came to question him, and to make sure that no one else said anything either. He was even asked to check the identity of any member of the Yeats family who visited the cemetery and, should anyone else ask questions, to say that his duties did not permit him to reveal the whereabouts of any grave. The abbé agreed.

When, three months later, Shackleton and Dulac read in the Times details of the arrangements for the poet's exhumation and reburial in Ireland, they wrote to his widow, George Yeats, told her what they had found out and tried to persuade her to abandon the plan. They didn't feel they could rely on the abbé's discretion and were worried that another body might be substituted for Yeats's to avoid a scandal. George Yeats contacted the French ambassador in Ireland and seems to have been content with his assurances that there would be no difficulty in returning her husband's remains. On March 31 1948, Abbé Biancheri again wrote to Dulac saying that, though he himself had been unable to attend the exhumation on March 17, Reynault, Lottier, a police inspector from Paris, the mayor of Roquebrune and a nameless "medical expert" had all been present. A body now lay in a casket in the chapel of rest and, despite the doubts, would be taken to Drumcliffe churchyard.

More than 20 years later, in the early 1970s, John Ormond Thomas, now working for the BBC in Cardiff, arrived at my mother's house wanting to speak to my grandmother. He was trying to trace the mysterious and avaricious Harley Street physician. He must have failed for nothing more was said until Souhami's book was published.

In October 1988, the Independent and the Irish Times carried a letter from Michael and Anne Yeats disputing Souhami's suggestion that their father had been buried in a pauper's grave. Their mother, they said, was an "extremely able and efficient woman, speaking excellent French" and would never have made such a mistake "on a matter of such crucial importance".

"In preparation for the ultimate transfer to Ireland, the remains were exhumed in March 1948 and placed in a chapel of rest. Careful measurements were made of the remains... and the task of certification was made easier by the fact that due to a long-term hernia problem, our father wore a truss. The exhumation took place in full conformity with the rigorous French laws on these matters, and in the presence of the mayor of Roquebrune, senior police officials, a medical expert, the superintendent of graves and other persons of official and expert standing."

They were, they said, "satisfied beyond doubt" that there had been no confusion. My mother's reply was printed a few days later. "Amongst my family," she wrote, "it is the belief that the body which lies in Drumcliffe cemetery is that of my mother's brother, Alfred George Hollis. My family, including myself, went to Roquebrune in 1947 and found that the bodies of my uncle and of WB Yeats had been exhumed, and on a search of the cemetery neither grave was found. Investigations by journalists discovered that identification of the body sent to Ireland rested on it being encased in a steel corset such as my uncle wore, and was buried in, as his frame was bent double by disease. My father exchanged letters with Michael Yeats explaining this, but the matter was dropped because of distress caused to both families."

When I was a child this story was part of the romantic mystery of my mother's girlhood. But her recent death made me more curious. Discovering things about her life has meant uncovering the lives of those she was close to and sometimes those she never met.

As Yeats himself once wrote:

Though grave-diggers' toil is long,

Sharp their spades, their muscles strong,

They but thrust their buried men

Back in the human mind again.

 This is an edited version of an article that first appeared in the London Review of Books. For subscriptions call 020-7209 1141.