Russell Brand will face "hell on earth" inside HMP Wandsworth, a former inmate at the London prison has said.
Brand, 51, was convicted a week ago of one count of rape and three counts of sexual assault and was sentenced on Monday to 10 years and six months in prison.
He is currently being held at the South London jail, which is one of England's largest Victorian-era prisons.
Chris Atkins, who served eight months at HMP Wandsworth for tax fraud, described the prison as "hell on earth".
He continued: "The first month is hands-down the worst. The mental shock is absolutely colossal. It was colossal for me and it's going to be 10 times worse for him because of the nature of his offences and the height from which he's fallen.
"He has to come to terms with it and the pure physical shock of suddenly being trapped in a dungeon for weeks on end with nobody to talk to most of the time is ghastly."
Wandsworth prison is by far the worst I've visited
The Russell Brand I saw in court was not the flamboyant character most people will know
A source close to the disgraced comedian said he was doing "remarkably well considering the circumstances"
