Joanna Mjadzelics, 38, was arrested as part of a worldwide investigation into Watkin's illegal activities against children.
The Lost Prophet's singer was jailed at the end of last year for 35 years after he was found guilty of a string of sex offences, including the attempted rape of an 11-month old baby.
RBS worker Mjadzelics met Watkins through MySpace when she was trying to get tickets to one of his concerts. They had an on/off relationship from 2006 until the time of his arrest.
The former call girl gave an interview with the BBC in recent weeks to discuss how she had gone to the Police several times four years ago when she discovered he had indecent images of children in his possession.
She said: 'It was repeated calls about the same little girl. Every time I knew that my complaints weren't going anywhere with the police. I would back it up by going to social services and saying "can't you do anything about this?"'
The former flame also added that Watkins had told her how he planned to rape a 2-year-old, and that he actively abused his power over super-fans and their children.