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An undated file photo of American author Sylvia Plath. Ted Hughes's previously unpublished poem detailing the weekend of her death is to be published. (Associated Press)

London magazine The New Statesman will publish a previously unseen poem by Ted Hughes that details the night his estranged wife, Sylvia Plath, killed herself.

Titled The Last Letter, the poem begins: "What happened that night? Your final night."

It then tells the chronology of the last weekend of Plath's life, when she and Hughes were still married but living apart.

British poet Hughes and American-born Plath are considered among the 20th century's greatest poets. Their stormy relationship has been the focus of decades of critical attention.

Plath earned a cult following through the novel The Bell Jar, whose descriptions of a suicidal young woman foreshadowed her own death, which followed only a month after its publication in 1963.

Plath's death shadowed Hughes for the rest of his life and he made only fleeting references to it in his own published work.

The poem was read out on Britain's Channel 4 on Wednesday by Melvyn Bragg, guest editor of the New Statesman. It is to appear in print on Thursday.