Terence ‘Tez’ Papworth was due to go on trial next week, accused of murdering Doncaster mum Amy-Leanne Stringfellow at a house in Balby in June.
But Papworth was found dead at HMP Leeds on Sunday, just days before he was due to appear at Sheffield Crown Court.
But Amy-Leanne’s mum Jacquie Fareham has asked people to take into consideration Papworth's family and said: “He was a son and brother.”
Writing on Facebook yesterday, she posted: “The police are on the way to give us official news.
"Can I please ask that before you make comments that you take into account that this evil man was a son and brother.
"Please take into consideration his poor mum and her feelings. Thank you in advance.”
Unconfirmed reports suggest that the 45-year-old was found dead in his cell.
Papworth had been due to stand trial at Sheffield Crown Court on November 30 and had recently appeared in court via video link for a case management hearing.
He was accused of murdering the 26-year-old at a house in Dryden Road, Doncaster after she was found critically injured at about 11.35pm on June 5.
She was pronounced dead at the scene shortly after emergency services arrived.
Amy, who was described as ‘beautiful and kind’ by distraught loved ones, was also a former soldier who had served in Afghanistan.
No further details of Papworth’s death have yet been released.