Wife Penelope Jackson lived with her "arrogant bully" husband for years before stabbing him to death, his brother claims as he has vowed to visit her in prison.
Jackson, 66, killed David, 78, in the kitchen of their Somerset home before calling 999 and telling them: "I thought I'd get his heart but he hasn't got one."
The retired accountant told Bristol Crown Court she had lost control during the lockdown in February after she says she was subjected to years of emotional and physical abuse.
She pleaded guilty to manslaughter but jurors convicted her of murder and she was sentenced to jail with 18 years behind bars minimum.
David's brother has now come forward saying they saw Jackson get abused.
Alan Jackson, his younger brother, has said he will visit Jackson in prison so "she's not on her own".
Alan told The Sunday Times : "I want to say to her, ‘What you’ve gone through I can quite imagine.
"I know what he was like towards me and my wife. You’re not on your own’."
The former mechanic has spoken out in defence of his sister-in-law, describing his brother as an "arrogant bully" who could become "very violent" after having a drink.
The 75-year-old also said David hid behind a "Mr Nice Guy" mask.
Alan said he used to have a close relationship with David, but says it all changed when David joined the army and started drinking.
Alan was not contacted by police or called to give evidence but had said he would be willing to testify if he was asked.
He added: "The poor woman never had anybody to stand by her side and say, ‘Hang on, she’s not as bad as you’re trying to make her out to be’."
Alan, who lives in Worcs., says their relationship soured in recent years because of the fallout over their mother's care and inheritance.
Alan said: "No one deserves to die the way he did but I can believe Penny would have been pushed to her limits.”
Alan and David's sister has also spoken to the press, but she has given a very different account.
Jennifer told the Mail on Sunday that there 'was only one bully in the relationship and it was Penny'.
The claims come as Jackson's lawyers are preparing to launch an appeal against her conviction.
It is understood they could attempt to argue the jury failed to take into account the suggestions that David subjected Jackson to coercive control throughout their marriage.
The appeal must be launched within 28 days.
It took the jury 11 hours to deliberate on its verdict which when delivered led to a gasp from the public gallery.
During the two-and-a-half-week trial, the jury heard the Jacksons had rowed about the defendant serving bubble and squeak with a gourmet meal bought for them by their daughter during the lockdown.
The victim and defendant had eaten the meal with Isabelle and Tom over Zoom.
The latter couple both said the row seemed to have blown over but added they had ended the call when the Jacksons began arguing over who had failed to charge their computer properly.
Jackson described taking a knife from the kitchen before she "lost all control" and stabbed her husband three times.
In an 18-minute phone call to emergency services, she told the call handler her husband was "bleeding to death with any luck" on their kitchen floor.
Judge Martin Picton remarked she had shown "not a shred of remorse" for her actions as he sentenced her.
