The partner of WikiLeaks founder Julian Assange has revealed that she had two children with him while he was living inside the Ecuadorian embassy in London.

Stella Moris, 37, a South African-born lawyer, issued a plea for the father of her two young sons, Gabriel, three, and Max, one, to be released from prison and said there were genuine fears for Assange’s health.

Assange was forcibly dragged out of the embassy and arrested in April last year, after Ecuador revoked his political asylum and invited Metropolitan police officers inside their Knightsbridge premises. He had been living at the embassy for nearly seven years.

Assange has been held in Belmarsh prison in Londonsince being given a 50-week jail sentence for violating his bail conditions. He is awaiting an extradition hearing on 18 May on behalf of the US, where he faces multiple charges under the Espionage Act over the activities of WikiLeaks.

In a statement to the courts supporting an application for bail, Moris revealed that she met Assange in 2011 when she was a legal researcher and looking into ways to halt Assange’s extradition.

“Over time Julian and I developed a strong intellectual and emotional bond. He became my best friend and I became his,” she wrote.

In 2015, Moris and Assange began a relationship despite the “extraordinary circumstances”, she said, and became engaged in 2017.

She said she had gone to great lengths to protect the couple’s children from the climate that surrounds Assange, adding that she was making the statement now because their lives were “on the brink” and she feared Assange could die.

According to Moris, Assange is in isolation for 23 hours a day and all visits have stopped.

“My close relationship with Julian has been the opposite of how he is viewed – of reserve, respect for each other and attempts to shield each other from some of the nightmares that have surrounded our lives together,” Moris said.

Julian Assange’s partne,r Stella Moris, and their sons Gabriel and Max. Photograph: Juan Luis Passarelli/PA

In an interview with the Mail on Sunday, Moris said Assange had watched the births of both children in London hospitals via live video link and met Gabriel after he was smuggled into the embassy.

She further revealed that both boys had visited their father in prison, and that the couple were planning to marry, whether Assange is released or not.

Friends and supporters of Assange, among them celebrities including Pamela Anderson, have said he has been in poor health for many months and have expressed growing concern for his wellbeing since the coronavirus outbreak.

HMP Belmarsh has repeatedly come under scrutiny in recent years, lastly after a remand prisoner was found dead in his cell in January, triggering an investigation by the prisons and probation ombudsman.

The man was the third prisoner to have died in Belmarsh within the past year. Another inmate was found dead there in November.

A judge at Westminster magistrates court rejected the request for an adjournment of Assange’s extradition hearing in May until September over what his legal team said were “insuperable” difficulties preparing his case because of the Covid-19 pandemic.

• This article was amended on 15 June 2020 to clarify details of Julian Assange’s imprisonment at HMP Belmarsh, and to make clear that he has been indicted by the US courts on espionage charges.