The elusive “Mr X” is being held for unspecified crimes and confined in total seclusion within a private wing of the maximum-security Ayalon prison.

No one knew of his existence until the shroud of secrecy was briefly lifted after a story appeared on the website of Israel’s leading Hebrew-language newspaper Yediot Ahronot.

Quoting unidentified officials within the Israeli penitentiary service, it disclosed that Mr X was being held in Unit 15, a wing of Ayalon prison that contains a single cell.

He is not though to receive any visitors and his wing is cut off from the rest of the prison by double iron doors. So hermetic are the conditions in which he is held that other prisoners can neither see nor hear him.