Georgette Civil - whose son got divorced from Amy in 2009 after two turbulent years of marriage - thinks Blake, who is currently serving 32 months in prison for burglary and possession of an imitation firearm, needed to take responsibility for the late singer's problems with drug abuse.
In an interview with UK TV show 'Daybreak', she said: "I think he has to take his portion of blame.
"I can't say whether or not Amy did drugs prior to meeting Blake, I can't. I think that's something that nobody will ever really know. But yes, in my heart I think that Blake has to take a portion of blame."
After Amy was found dead in her home in Camden, north London, on Saturday afternoon (23.07.11) at the age of just 27, Georgette voiced her fears that heroin addict Blake would "kill himself" when he found out about the tragedy.
She said at the time: "Blake will kill himself. He won't make it without her. He will be devastated, totally and utterly devastated. He'll go straight back to self-harming. I'll have to ring the prison and he'll have to be put on watch.
"He was always ringing her and she was always ringing him. Blake always wanted her back. She couldn't walk away from him and he couldn't walk away from her. Her and Blake were both lost and we handled it badly."
Meanwhile, Blake's current girlfriend Sarah Aspin - who is mother of his newborn baby son Jack - admitted the divorced pair were "soulmates".
Sarah explained: "He is devastated and shattered. He just can't take it in that she's dead and he'll never see her again. Blake is the father of our son. But I saw him and Amy together and I know they were really in love and they were soulmates.
"She always loved him and he always loved her - but it was just never going to work. Basically they couldn't live with each other and they could not live without each other. It is hard for me knowing he still loved her, but I do understand his feelings."
The 'Back to Black' singer is due to be cremated today (26.07.11) in accordance with Jewish custom, despite an inquest not being able to yet determine her cause of death.