The brother of former EastEnders actress Gemma McCluskie endured months of abuse from her, culminating in her threatening him with a knife, a court has heard.
Tony McCluskie, 35, said his sister's behaviour had become volatile and she regularly shouted at him and called him names.
McCluskie admits killing the 29-year-old at the flat they shared in Shoreditch, east London, on March 1, 2012 but denies murder.
He told an Old Bailey jury he had no recollection of killing her or dismembering her and dumping the body in a canal.
McCluskie said the last thing he remembered was grabbing his sister's wrists as she threatened to stab him.
Her torso was found in a suitcase in the Regent's Canal in east London and her limbs in plastic bags. Her head was found six months later.
Police have released CCTV footage which shows McCluskie dragging a large bag into the boot of a taxi. In another clip, he is seen dragging a large bag along the Regent's Canal.
The actress, who played Kerry Skinner, the niece of Ethel Skinner, in the BBC soap in 2001, was officially identified by dental records.
The prosecution at her brother's murder trial said pot-smoking McCluskie bludgeoned his sister to death after a row about an overflowing sink.
McCluskie told the jury he had left a tap on, sparking a row and prompting his sister to call him later in the day and demand he moved out.
Later when they were both back in their flat in Pelter Street, the argument continued and his sister came at him with a knife after hurling a string of abuse, he said.
McCluskie, wearing a tie and glasses, told the court she had threatened to stab him and his on-off partner Terri Arnull, and to make sure Ms Arnull's son, who he viewed as his own, was taken into care.
"I got very angry, I just couldn't believe what I was hearing. All I remember is just grabbing her wrists. After that I have no recollection."
He said the next thing he remembered was waking up two days after his sister's death.
"I have tried countless times, even now I lie there all night and sit there all day trying to work out what happened, have the answers to every question that everyone has for me.
"All the questions from my family, they deserve to know, and me also, I need to know what happened, what made me do such a thing."
The court heard his defence is one of lack of intention, as well as loss of control.
McCluskie said despite her bubbly exterior, behind closed doors his sister was often abusive, shouted at him and called him names.
He told the court that prior to her death he had split from his partner, his mother was undergoing treatment for a brain tumour and he was under great pressure at work because some colleagues thought he had reported them for breaching health and safety guidelines.
"I was pretty messed up with everything that was going on," he said.
McCluskie described his sister as a "very strong personality, outgoing, a very fiery person", but said loving texts between them presented to the court were very different from the way she often treated him.
"There would be nastiness coming out, hostile, threats, shouting and name-calling, I would say about my appearance, the way I looked."
The case continues.