A two-year-old boy allegedly battered to death by his mother and her boyfriend was told “you have to ruin the fun” by one of his killers during an assault in the weeks before he died, a court heard.

Prosecutors say Kyrell Matthews was repeatedly struck by his mother, Phylesia Shirley, and her then-partner, Kemar Brown, over several weeks, with “harrowing” secret audio recordings capturing the violence said to have been meted out by the pair in Shirley’s one-bedroom flat in south London.

Kyrell, who was non-verbal, was found to have 41 rib fractures by the time he died on October 20 2019, as well as internal bleeding and a 1.6in (4cm) cut to his liver.

The pair deny murder.

Prosecutor Edward Brown QC told jurors at the Old Bailey: “Kyrell had his ribs crushed or broken by blows within the four weeks before October 20.

“At least one of the defendants plainly inflicted a significant number of injuries in at least five separate incidents in the four weeks leading up to … Kyrell’s death.

Your Local Guardian: Elizabeth Cook of Phylesia Shirley, and her partner, Kemar Brown, appearing at the Old Bailey in London charged with murder and causing or allowing the death of a childElizabeth Cook of Phylesia Shirley, and her partner, Kemar Brown, appearing at the Old Bailey in London charged with murder and causing or allowing the death of a child

“The pain and distress in those four weeks when he was abused was brought vividly to the fore by those harrowing recordings.

“On October 20, his ribs were crushed once more – it killed him.”

Police later discovered secret audio files on Shirley’s mobile phone – the apparent results of attempts to catch Brown being unfaithful – which inadvertently captured the abuse, the prosecution said.

They included multiple audio files where it appeared Kyrell was hit repeatedly, with Brown saying “shut up”, causing the toddler to cry and scream.

On another occasion, prosecutors said, Brown inflicted several blows on the little boy before telling him: “You have to ruin the fun.”

Another file, the prosecution said, captured Shirley striking her own child and causing him to cry in distress.

The prosecutor said Shirley wanted to remain in a relationship with her partner, despite knowing he was abusing her son.

He said: “Indeed, you may well conclude that she joined in the abuse.

“She was prepared to reject what should have been motherly care in protecting Kyrell in favour of abuse by her – his own mother – and in favour of the abuse carried out by a man she knew was abusing her child.

“The truth is that his death came when once more he was abused in that flat, once more in a very similar way, causing very similar injuries, except on this occasion it was so much more serious, the abuse and the results were catastrophic.”

Jurors heard that the toddler did not attend a nursery and so was in the full-time care of his mother, then aged 21, and that neither defendant was employed in the period leading up to Kyrell’s death.

Both also said they left the flat at separate times, briefly, the day the boy died – although only Shirley’s account could be corroborated by CCTV.

Shirley, 24, and Brown, 28, of separate addresses in Thornton Heath, deny murder.

Brown also denies two further charges – causing or allowing death, and causing or allowing serious physical harm to a child.

Mark McDonald, for Brown, told jurors his client’s case will be that the injuries inflicted were the result of incorrect advice from NHS 111 on how to resuscitate the boy.

Shirley has admitted allowing the death and allowing serious physical harm to a child.

The trial continues.