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A married doctor who had a close friendship with baby killer Lucy Letby and gave evidence against her at her trial has died.

The registrar, described as the former neo-natal nurse's 'boyfriend' by prosecutors, worked alongside the child killer at the Countess of Chester Hospital in 2016, two years before she was first arrested.

Letby denied being in a relationship with the medic and instead insisted he was simply her 'best friend.'

But she referred to him as 'sweetie' in texts and notes found at her home also described him as 'love.'

She also broke down and cried in the dock at Manchester Crown Court when he was called to give evidence against her.

Sources said the doctor, who was in his 50s, later moved to work at a different hospital.

He had been ill before his death last month. His funeral has since been held.

The medic successfully applied for anonymity during Letby's ten-month trial and was referred to in court as Doctor A.

Prosecutors claimed Letby's infatuation with the registrar was one of her motivations for harming babies because she knew he would rush over to help when one of them became seriously ill.

The court heard Letby went to London with the doctor and the pair also enjoyed walks and days out together.

A married doctor who Lucy Letby called her 'love' in private notes before he testified against her in court has died

The registrar worked alongside the child killer in 2016, two years before she was first arrested. Pictured: Lucy Letby

The pair also exchanged more than 1,300 Facebook messages over three months in 2016.

In one the doctor told Letby she was 'one of the few nurses I would trust with my own children', the court heard.

In evidence to the public inquiry investigating Letby's crimes, in 2024, the medicsaid he had been 'misled' and 'maybe manipulated' by her.

Letby was found guilty of murdering seven babies and attempting to kill seven more between June 2015 and June 2016.

She is serving a whole-life order at Bronzefield Prison, Surrey, but maintains her innocence.

The Criminal Cases Review Commission is considering evidence presented by a panel of doctors claiming that natural causes and poor care were to blame.