When paramedics arrived at the scene last year, they found bruises all over the little girl’s body, including her head, neck, abdomen, back and private parts; there was blood in her nappy and sick on her face.

Isabelle was not breathing and was cold to the touch as medics battled in vain to save her, and she died the next day in hospital.

A post mortem revealed the extent of her injuries – that her skull was fractured, her brain damaged and that she had been sexually assaulted.

Experts told the jury that Isabelle had been shaken and her head had impacted against a wall or the floor.

Just 11 days before her fatal collapse, Isabelle was taken to her GP and then to hospital with a broken leg. She was then discharged to her mother, who had shown aggression towards medics when concerns were raised about what had happened.

Richard Wright KC, prosecuting, told the court: “For weeks this child had been violently assaulted and her death, by that terrible head injury, was simply the end point in that campaign of violence to which she had been subjected.”

Walker had suffered from domestic violence previously and had two cameras installed in her home, which proved that Isabelle suffered a broken leg while in the sole care of Simpson.

Simpson also bathed Isabelle without Walker’s permission while he supposedly looked after the two-year-old during her mother’s hospital appointment.

Kirstie Devine, of the Crown Prosecution Service, said: “The prosecution presented a raft of evidence including pathology reports, expert medical evidence, CCTV from the home, records of text messages and phone conversations that showed only the two adults who were regularly with Isabelle could have harmed her.”

Senior Investigating Officer, Detective Chief Inspector Steve Chatterton of Cleveland Police, added: “Isabelle suffered catastrophic injuries at the hands of the very people who should have loved her, cared for her and protected her.

“Her life was cruelly taken in the most tragic and heart-breaking circumstances.”