The Belfast Telegraph reports that it is believed Mr Gilmour died of natural causes
It has been reported former IRA informer Raymond Gilmour has been found dead at his home in Kent in England.
According to the Belfast Telegraph, the 55-year-old's decomposed body was found in his flat.
A post-mortem examination is due to be carried out, with his funeral expected to take place next week.
It is reported that friends believe he died of natural causes.
Raymond Gilmour joined the Irish National Liberation Army (INLA) in the mid-1970s, while also acting as a police agent. He later joined the IRA.
He ultimately gave evidence in a trial of more than 30 IRA suspects.
The trial collapsed in 1984, and Mr Gilmour was resettled in England by MI5 under a new identity.
Mr Glimour had spoken of his desire to return to Northern Ireland and his battle with alcoholism.
He published two books about his experiences.