An investigation has been launched after an inmate died at Belmarsh prison.
The Ministry of Justice (MoJ) confirmed a prisoner had died on Monday and an investigation was under way.
Stella Moris, the partner of WikiLeaks founder Julian Assange, spoke out about the incident.
She said the man was being held on the same wing Assange in the high-security jail in south-east London and they were friends.
In a post on Twitter she claimed the man was a Brazilian named Manoel Santos, who had lived in the UK for 20 years and had been served with a deportation notice by the Home Office.
She added: “Julian wants to express his condolences to Manoel’s friends and family.
“Julian tells me Manoel was an excellent tenor.
“He helped Julian read letters in Portuguese, and he was a friend.
“He feared deportation to Brazil after 20 years, being gay put him at risk where he was from.”
A Prison Service spokeswoman said: “The Prisons and Probation Ombudsman has been informed following a death in custody at HMP Belmarsh on 2 November.”
The Home Office has been contacted for comment.