The ex-girlfriend of a former boy band star and her boyfriend who were convicted of murdering and burning their French nanny in a bonfire as they barbecued chicken were sentenced Tuesday to at least 30 years in prison.

Sabrina Kouider, 35, and Ouissem Medouni, 40, were convicted last month of killing their child’s nanny, Sophie Lionnet, 21, at their south London home in September 2017. Each had denied the murder and blamed the other.

Prosecutors said the pair killed Lionnet after becoming obsessed with the belief she was conspiring with Kouider’s ex-boyfriend Mark Walton, a founding member of Irish boy band Boyzone.

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Kouider was said to be fixated on Walton and believed Lionnet was having an affair with him and helping him carry out a sex-abuse plot — though the two had never met. Kouider, a fashion designer and Medouni, a banker, repeatedly beat and interrogated Lionnet in an attempt to make her confess.

Prosecutors claimed the couple starved Lionnet, beat her with an electrical cable and tortured her by dunking her head underwater. After killing her in a bathtub in September, they threw her body on a bonfire in their yard in an affluent area of southwest London near the home of the Wimbledon tennis tournament as they barbecued chicken nearby.

When neighbors called firefighters because of the pungent-smelling smoke, Medouni claimed the charred remains belonged to a sheep. Lionnet’s body was found on Sept. 20, 2017.

Walton, who is now a music producer in Los Angeles, said in court in March that his two-year relationship with Kouider was “the most turbulent relationship I had ever been in.”

He described in court how she would sometimes "flip, get very angry, very loud and just not care where we were. She would just go crazy over something trivial."

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At London's Central Criminal Court, Judge Nicholas Hilliard sentenced Kouider and Medouni to life with no chance of parole for 30 years. He said the pair was guilty of "horrible cruelty."

"The suffering and the torture you put her through before her death was prolonged and without pity," the judge said.

The Associated Press contributed to this report.