The Times of London says in Monday editions that Nicholas Hughes hanged himself at his home in Alaska. The 47-year-old was not married and had no children of his own.
The newspaper says his sister, Frieda, confirmed his death. Ted Hughes' publisher in London, Faber and Faber, says she has arrived in Alaska.
The death adds another chapter to the family's tragic history. Plath committed suicide in 1963, shortly after her turbulent relationship with Ted Hughes ended. Her son had just turned 1 year old.
Ted Hughes had left her for another woman, and spent years battling feminists who blamed him for her death.