The incident comes less than a month after paedophile singer Ian Watkins was stabbed to death at the same prison.
Three prisoners have been arrested on suspicion of murder after a child killer was found dead in his cell.
The Prison Service confirmed the man was 33-year-old Kyle Bevan, who was jailed for life for murdering his partner’s two-year-old daughter Lola James in Haverfordwest, Pembrokeshire, in 2020.
Bevan was set to spend at least 28 years behind bars for the savage killing after inflicting catastrophic head injuries on the toddler during a six-hour attack.

Officers were called to category A HMP Wakefield at 8.25am on Wednesday following reports of a man being found dead in his cell, West Yorkshire Police said.
The force said his death was being treated as “suspicious”, with investigations continuing.
“Three men, who are all serving prisoners, have been arrested on suspicion of murder,” a statement said.
The incident comes less than a month after paedophile singer Ian Watkins was stabbed to death at the same prison.
Lola James’ injuries were so severe they were likened by doctors to a high-speed car crash, with 101 scratches and bruises on her tiny body and evidence of weapons being used.
The girl’s death came months after Bevan, a prolific drug user, moved into the home within days of connecting with Lola’s mother Sinead James on Facebook.
Bevan, from Aberystwyth, Ceredigion, had denied murdering Lola but was convicted in 2023.
A Prison Service spokesperson said: “HMP Wakefield prisoner Kyle Bevan’s death was confirmed on 5 November.
“We are unable to comment further while the police investigate.”

Former Lostprophets frontman Watkins, 48, died from a stab wound to the neck at the prison, an inquest opening heard.
Inmates Rashid Gedel, 25, and Samuel Dodsworth, 43, have been charged with murdering him.
Two more men from the prison have been arrested on suspicion of conspiracy to murder.

