IRA informer Raymond Gilmour has been found dead at his home in Kent, according to reports.
The Belfast Telegraph has reported that the 55-year-old's body was found in his flat by his 18-year-old son from his second marriage.
A postmortem is due to be carried out with his funeral to take place next week.
Mr Gilmour, from Derry, gave evidence against 31 men and women in a major Northern Ireland supergrass trial but after the case collapsed in 1984 he was given a new identity by MI5 and resettled in England.
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He is said to have suffered from alcoholism and psychological problems.
He had no contact with his wife and two children but married twice again in England.
PA