There were doubts about the authenticity of WB Yeats’s bones even before they were transferred from France for reburial in Drumcliffe churchyard in September 1948.

Aware that the poet’s remains had been scattered in an ossuary in 1946, Yeats’s friends attempted to dissuade his widow, George, from going through with the repatriation. At the ceremony in Co Sligo the poet Louis MacNeice protested that the shiny new coffin transported by the Naval Service was more likely to contain “a Frenchman with a club foot”.

Recently discovered French documents have driven the last nail into the coffin. They constitute compelling evidence that the bones gathered in Roquebrune-Cap-Martin, the Riviera town where he died in 1939, were little more than a haphazard assemblage.

Bernard Cailloux, the French diplomat who was sent to Roquebrune to locate Yeats’s missing remains early in 1948, nine years after the poet’s death, reported that it was “impossible to return the full and authentic remains of Mr Yeats” and proposed asking Dr Rebouillat, the local sworn pathologist, “to reconstitute a skeleton presenting all the characteristics of the deceased”.

At best, Cailloux wrote, it might be possible to find “an iron corset, a skull, and perhaps a Bible”. Yeats had an unusually large skull, so it is conceivable that his skull was actually found and sent to Ireland.

Alfred Hollis, an Englishman who died around the same time as Yeats, and who was initially buried next to him, wore a steel corset for spinal tuberculosis. In his certificate of exhumation from March 20th, 1948, Rebouillat based his reconstitution of Yeats’s skeleton on “the presence of a thoracic corset”. Yeats’s son, Michael, said he wore a leather truss for a hernia.

Hollis’s family have long claimed that it was he, not Yeats, who was sent for burial in Sligo. The French documents indicate it’s more likely that the remains were those of several people, chosen for their size from bones that were sorted by type into piles of, for example, skulls, fibulae and tibiae.

Subsequent diplomatic correspondence refers to Cailloux’s report, strongly implying that his recommendation to assemble a skeleton, from bones that Cailloux described as “mixed pell-mell with other bones”, was followed. The operation received the tacit acceptance of the Yeats family and the minister for external affairs, Seán MacBride, the son of Yeats’s great love, Maud Gonne.

“We can be assured of the discretion of the family and the Irish authorities,” Stanislas Ostrorog, the head of the French legation to Ireland, wrote to Jacques Camille Paris, the Europe director of the French foreign ministry, on August 12th, 1948.

Ostrorog added that “certain precautions must be taken on our side to avoid any indiscretion about the procedure undertaken a few months ago to obtain the remains of the poet . . . so that no administrative difficulties arise giving cause for suspicion; so that no inopportune explanation is given to the Irish present at the ceremony”.

Yeats died at the Hôtel Idéal Séjour in Roquebrune on January 28th, 1939. “If I die, bury me up there” – in the churchyard at Roquebrune – “and then in a year’s time when the newspapers have forgotten me, dig me up and plant me in Sligo,” he instructed his wife.

The second World War prevented George from carrying out Yeats’s instructions. In June 1947 the poet’s last lover, the journalist Edith Shackleton Heald, and her lover Hannah Gluckstein, the painter known as Gluck, decided to visit Yeats’s tomb. They were appalled to learn from the local curate that Yeats had been disinterred the previous year and his bones mixed with others in the ossuary.

In her 1988 biography of Gluck, Diana Souhami recounted how Heald crouched on the floor of their hotel in Monte Carlo, sobbing and saying, “I would know his bones anywhere.” Gluck and Yeats’s friend Edmund Dulac conspired to cover up the dispersal of Yeats’s remains. “All it would take would be an excessively curious tourist for the press to batten on to this with avidity and we must at all costs avoid the scandal that would arise from such a revelation,” Dulac wrote to the curate, Abbé Biancheri.

The publication of Souhami’s book led to bitter exchanges via newspaper columns between the Hollis and Yeats families, who eventually called a truce to avoid mutual distress.

Letter to The Irish Times, October 6th 1988

In January 1948 the Times announced that George Yeats intended to repatriate the poet’s remains. Dulac and Gluck both wrote to her in protest. Gluck recounted the painstaking research she had conducted and concluded that “these remains would be almost impossible to find, and if found, identity would be open to doubt”.

Ostrorog, the French ambassador in Dublin, wrote to Paris, the Europe director at the foreign ministry: “A few months ago, the poet’s son came to see me to tell me, under the seal of secrecy, that they are unable to find the poet’s remains in the Roquebrune cemetery where the inhumation had taken place in 1939.”

If not handled carefully, Ostrorog warned, the case “risks causing us serious trouble . . . I was most anxious to resolve the issue, for if the family and the Irish legation were obviously guilty of negligence, the French authorities could also be taken to task if it were known that this great foreign poet, who had spent so many years of his life in France, had been thrown into a communal grave.

“As you know,” Ostrorog continued, “an investigation was first carried out by Mr Cailloux, sent specially by the cabinet. Following this, the remains were collected and placed in a coffin.”

On March 20th, 1948, Cailloux went with five other men to the ossuary for the exhumation. Cailloux had suggested that Dr Rebouillat reconstitute a skeleton. When Rebouillat drafted the certificate of exhumation he wrote that “recognition was established with certainty and precision . . . These bones were . . . placed in the coffin which was closed, soldered and sealed in our presence.”

Ostrorog then “summoned the young Yeats to inform him, without giving any details, that following an investigation, the mortal remains of his father had been collected and were currently in a coffin in Roquebrune cemetery. He thanked me wholeheartedly, avoiding asking for any other explanation.”

A few weeks later, Ostrorog continued, he met MacBride, who “expressed to me personally in the warmest terms his thanks for the care with which this affair had been resolved . . . We understood each other without it being spelled out. MacBride’s mother was formerly extremely close to the poet. There was obviously an interest that no incident would happen that could give rise to a press campaign.”

Philippe Benoist, described in correspondence as a young, intelligent and discreet diplomat who was “aware of the whole affair”, was selected to represent France at the removal. A French army honour guard escorted the coffin from Roquebrune cemetery to the town square for a lying-in-state. Draped in the Irish Tricolour, the coffin was carried on to the Irish corvette the LE Macha, in the port of Nice, to the strains of La Marseillaise and A Nation Once Again.

“It should notably be understood that if, by chance, the Irish were surprised to find themselves in front of a new coffin, we would explain that these measures were taken for the transport to Ireland,” Ostrorog advised. “The Irish ambassador in Paris will, no doubt, attend the ceremony. But he is not aware of anything. What purpose would it serve?”

Jacques Camille Paris classified his correspondence with Ostrorog, Cailloux’s report and Rebouillat’s certificate of exhumation as “personal correspondence”, an indication that he realised how sensitive they were. Paris took these documents with him to Strasbourg when he became the first secretary general of the Council of Europe.

When Paris died, in 1953, the trunk containing the documents was given to his widow, Reine, the daughter of the French writer Paul Claudel. She stored it in the Claudel family chateau, in Brangues, in southeastern France, where it was recently opened by Daniel Paris, the son of Jacques Camille and Reine.

Daniel Paris turned the documents over to the Irish Embassy in Paris in a discreet ceremony last month. The Embassy entrusted them to French foreign-ministry archivists, who will send high-quality facsimiles to the National Library of Ireland later this year.

The fact that the documents were kept in Claudel’s chateau adds an ironic twist to the story. Yeats and Claudel had met in the early 20th century at the Tuesday literary salon of the poet Stéphane Mallarmé. Both writers were interested in symbolism and Japanese Noh theatre. Yeats referred several times to Claudel in his works.

A verse in WH Auden’s poem In Memory of WB Yeats said that Kipling and Claudel, who like Yeats held right-wing political views, would be forgiven because they had written well. Auden later deleted the verse.

The French diplomats who organised the sham remains in the hope of pleasing the Yeats family and the Irish government wove a tangled web. The facts so long hidden in Jacques Camille Paris’s trunk sit uneasily with the visit of reconciliation that Prince Charles and his wife, Camilla, made to Yeats’s grave in Drumcliffe churchyard in May.

The Yeats family, the Church of Ireland and the Sligo tourism industry are unlikely to welcome the news, especially amid celebrations of the sesquicentenary of Yeats’s birth.

Contacted by The Irish Times, the poet’s granddaughter and closest surviving relative, Caitriona Yeats, did not wish to comment, and referred us to the letter to the editor of the newspaper by Yeats’s children, Anne and Michael, published on October 6th, 1988.

In her book George’s Ghosts: A New Life of WB Yeats, from 2000, Brenda Maddox suggested that “an analysis of the DNA of the bones buried at Drumcliffe would swiftly settle the matter with absolute finality”. Irish officials shudder at the mere mention of DNA. For as Prof Warwick Gould, of the Institute of English Studies at the University of London, says, Yeats’s grave is a shrine, and “shrines are about stones, not bones. Their symbolic significance designedly outlives human remains, which rot.”

When Yeats wrote Under Ben Bulben, in the last month of his life, Gould says, the poet intended that his grave should provoke thought. The original draft read:

Draw rein; draw breath

Cast a cold eye

On life, on death:

Horseman, pass by.

So Yeats placed himself in the tradition of the siste viator signs on Roman roadside tombs. “The Latin words mean ‘Stop, traveller,’ ” Gould says. “They invite private reflection on what is graven upon funerary stones.”

Devout Yeatsians say it doesn’t really matter whose bones lie beneath Benbulbin; no one doubts he wrote the poems. “I feel Yeats’s soul is in Thoor Ballylee,” says the US lawyer, Yeats scholar and benefactor Joseph Hassett, referring to the poet’s former home in Co Galway. “It’s less important where the body is.”