Boyzone founder Mark Walton reveals 'turbulent relationship' with ex accused of murdering French nanny

The founder of boy band Boyzone has revealed in court the "turbulent relationship" he had with his ex-girlfriend who is accused of murdering her French nanny.

Mark Walton, who created the Irish boy band in 1993, flew in from Los Angeles to give evidence at the Old Bailey trial of fashion designer Sabrina Kouider.

The 35-year-old mother and her partner Ouissem Medouni, 40, are accused of murdering au pair Sophie Lionnet and throwing her body on a bonfire at their home in Wimbledon, south west London.

Sabrina Kouider and her partner Ouissem Medouni are accused of murdering au pair Sophie Lionnet and throwing her body on a bonfire. Photo / Supplied

The couple had allegedly tortured the shy 21-year-old into "confessing" to being in league with Mr Walton.

However, Mr Walton said the first he knew of Miss Lionnet was when murder squad detectives contacted him in September last year.

He said Kouider had been "abusive" and "exhibited a manipulative and controlling nature" with a "calculating streak". He also described her as a "really gentle, sweet, loving" person who could become "quite scary" in seconds.

He told jurors: "Sabrina shared some stories from her past.

"I guess knowing that, I felt it brought us closer together at times, but it was turbulent, probably the most turbulent relationship I had ever been in.

"She would go from softly spoken French accent then she would flip, get very angry, very loud and just not care where we were. She would just go crazy over something trivial."

The wealthy music mogul supported her financially through the highs and lows of his successful career. After leaving Boyzone, he found success with Fifth Avenue and more recently as a judge on Vietnam Pop Idol.

The softly-spoken Irishman said he met Kouider in a NatWest bank in Notting Hill in 2011 and hit it off straight away.

He said: "I was in love. She was my life then so..."

He said he gave her thousands of pounds a month, paid for nannies and even covered £12,800 ($25,000) in rent after she had left him, the court heard. Yet Kouider then fired her nannies, and accused them of stealing or being attracted to her "friendly" boyfriend, it was alleged.

Mark Walton created the Irish boy band Boyzone in 1993. Photo / via Twitter

The musician said they lived together for two years in Queensway, London, before she disappeared and they split up.

After Mr Walton stopped paying her rent in 2014 when they split, she took out a non-molestation order claiming harassment, the court heard.

She also rang his mother in Dublin, contacted his business partners and created a fake Facebook page accusing him of being a "paedophile", he said.

Mr Walton told jurors: "I was broken, emotionally broken but I loved her."

The court has heard there is no truth in any of the accusations against him. Kouider and Medouni have admitted perverting the course of justice but deny murder.

The trial continues.