A fashion designer accused of killing her French nanny called her partner a "murderer" from the dock after he described a violent incident involving Blue star Duncan James.
Sabrina Kouider, 35, and Ouissem Medouni, 40, allegedly killed 21-year-old Sophie Lionnet and dumped her body on a bonfire at their Wimbledon home last September.
Jurors heard the mother-of-two became obsessed that Miss Lionnet was in league against her with her ex-boyfriend Mark Walton, founder of Boyzone.
Giving evidence, former Societe Generale financial analyst Medouni said he was "very concerned" for Kouider's mental state, having attacked him twice before.
But as he recalled a series of incidents, Kouider shouted at him from the dock, saying: "You are just a murderer. That's all you are."
The couple met at a French funfair when Kouider was a teenager and they went on to have an on-off relationship.
Medouni told jurors he still loved Kouider even after she started seeing Mr Walton in 2011.
He said he was "shocked" when she told him over a coffee he had "tried to strangle her".
She then struck up a friendship with members of the boy band Blue, in particular Mr James, who she said was "nice" and a "good friend", the court heard.
Orlando Pownall QC, defending, asked about an incident when police were called to Kouider's north London flat to reports of damage to the door.
Mr Pownall said the landlord complained she and a husband or partner had told him to "f*** off" and "threatened him with a crowbar".
Medouni said Kouider told him it was Mr James, who lived nearby.
Medouni told jurors Kouider was the "dominant" partner in their relationship and her moods would go "up and down very quickly in the space of seconds".
He added: "In the last years, every morning she would wake up screaming for nothing, and, if she had a dream about me being with another woman, she said it was going to happen and make up a story in her mind about it.
"She said she had a gift for knowing what is going to happen."
Medouni said he covered up for Kouider's mental instability with police and social workers as she became more obsessed with Mr Walton.
She was also "jealous" of him talking to Miss Lionnet, who was "very shy" and liked to read Harry Potter books in her room.
The defendant said Miss Lionnet earned £50 a week but the couple stopped paying her at the end of July last year because Kouider was "angry at her".
Around this time, Kouider attacked her as she was cooking, Medouni said: "She lost her temper and dragged her hair down. I recall she was going to hit her.
On what he told Kouider, he said: "It's crazy. It's an assault so don't ever do that again. She's got to go. I had a feeling it's going too far."
He told jurors: "To be honest I messed up. I should have bought a ticket and sent her home. I hate myself because there is this occasion and a crescendo after that. When I think about the whole situation, I'm really really angry with myself."
Medouni said it was Kouider's idea to question the nanny on tape to present evidence to police.
The interrogations which went on for hours focused on Kouider's belief Miss Lionnet had been meeting with Mr Walton, the court has heard.
Medouni and Kouider have admitted perverting the course of justice but deny murder.