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.

Letby called him her ‘best friend’ and ‘love’ in notes later found at her home, while the pair exchanged more than 1,300 Facebook messages over three months in 2016.

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, The Sun reported. His funeral has since been held.

During Letby’s trial, she was quizzed about her relationship with the doctor, whom prosecutors referred to as her ‘boyfriend’.

He successfully applied for anonymity during Letby’s ten-month trial to protect his family 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.

Read more: Married doctor who Lucy Letby called her ‘love’ in private notes before he gave evidence against her at trial dies