South Yorkshire Police is being investigated over its handling of complaints against convicted child sex offender Ian Watkins.
The force is under investigation by the Independent Police Complaints Commission over the handling of a complaint made against Lostprophets rock star Watkins last year.
The IPCC, which is already investigating whether or not South Wales Police acted quickly enough against Watkins, has said the inquiry follows a referral from the force in September.
Watkins is to be sentenced next month for offences including attempted rape of a baby.
A 21-year-old mother from Doncaster is to be sentenced alongside him for allowing the singer to abuse her own 12-month-old baby.
The woman, who cannot be named, pleaded guilty to a string of vile offences alongside Lostprophets singer Watkins and another mother aged 24 at Cardiff Crown Court last week.
She admitted aiding and abetting an attempted rape, aiding and abetting rape, two counts of sexually assaulting a child, taking indecent photographs of children and distributing indecent photographs of children.
The Doncaster woman and the other woman, from the Bedford area, are said to have been fans of Watkins’ band.
Watkins, 36, of Pontypridd, who was called a “determined and committed paedophile” in court, admitted attempted rape and sexual assault of a child under 13 but not guilty to rape - a plea the prosecution accepted.
He also admitted three counts of sexual assault involving children and six involving taking, making or possessing indecent images of children and one of possessing an extreme pornographic image involving a sex act on an animal.
All three convicts are set to be sentenced on 18 December.