A French nanny was beaten, killed and thrown on a bonfire after her employers accused her of being “in league” with a former popstar boyfriend, a court heard.

“Big hearted” Sophie Lionnet, 21, was starved, mistreated and violently assaulted after she went to live with mother of two Sabrina Kouider and Ouissem Medouni, the Old Bailey heard.

The pair, who are also French, allegedly confronted Miss Lionnet with “outlandish” allegations and kept her a prisoner in their home in Wimbledon, south west London.

Prosecutor Richard Horwell QC told jurors: “Sophie was trapped in a domestic nightmare.”

Kouider, 35, the former partner of original Boyzone band member Mark Walton, and Medouni, 40, have denied her murder in September last year.

The court heard “malevolent” Kouider accused her nanny of being in cahoots with Mr Walton and in rambling complaints said he controlled her through “black magic”.

She had also falsely labelled Mr Walton a paedophile using a fake Facebook account in 2015, the court heard.

But jurors were told the allegations against Miss Lionnet and the former Boyzone star were “quite untrue”.

Mr Horwell said: “At the centre of this trial is the fact that these inventions or beliefs, whatever they may have been, concerning Mark Walton formed a central part of the reason why the defendants murdered Sophie.”

The barrister told jurors Miss Lionnet had been “naive and particularly vulnerable” when she went to work for the defendants and was an “easy target” for abuse.

Her life in Wimbledon was “bizarre and oppressive”, the court heard.

She was hardly paid, starved, beaten and interrogated by her employers while being prevented from returning home to her family, jurors were told.

In notes, she described being called a “whore, a bitch and a slut” for no reason.

Kouider would shout and scream at Miss Lionnet and accused her of stealing a diamond pendant.

Mr Horwell told jurors the false allegations were “contagious” and Medouni was “beguiled” into adopting the same delusions.

Following her death, more than eight hours of “harrowing” recordings were recovered from the defendants’ mobile phones of Miss Lionnet being interrogated.

They depicted “a young emaciated, frightened and helpless woman anxious to say and do whatever her two tormentors wanted her to say”, the lawyer said.

Miss Lionnet was intimidated, threatened with imprisonment, rape and violence to exact some sort of “confession”, possibly to later embarrass Mr Walton, jurors were told.

The prosecutor said: “The last days and hours of Sophie’s life must have been truly wretched.

“She was subjected, at times, to a brutal and oppressive inquisition and to significant violence”.

She suffered fractures to her sternum, ribs and jawbone, but the exact cause of her death was unknown due to an attempted to dispose of her body.

“The defendants burnt her body in the garden of their home in the hope that no one would ever discover her remains.

“Their plan was to dispose of Sophie’s body and to explain her disappearance by inventing a story that she had left their employment under something of a cloud.

“But their wicked plan was frustrated by the combination of a neighbour and inquisitive fire fighters,” Mr Horwell said

The victim’s parents sat in the well of the court as the case was opened.