"But despite his battles with drugs, his egotistic behaviour and the resulting fractures and frustrations within our band, we never imagined him capable of behaviour of the type he has now admitted."
Watkins pleaded guilty to sexually touching a one-year-old and encouraging a groupie to abuse her own child during a webcam chat.
The 36-year-old, from Pontypridd, south Wales, also admitted possessing and making child porn as well as launching the plot to rape a baby.
The remaining band members announced in October that they had split up.
Their statement went on: "We are heartbroken, angry and disgusted at what has been revealed. This is something that will haunt us for the rest of our lives.
"Being in a band has always been a labour of love and a platform to inspire people, not to take advantage of them.
"It's still hard to believe this is happening and that someone we were once so close to has destroyed so many lives, lying every step of the way."
They added: "Our hearts go out to Ian's family, the fans and friends he betrayed, and most importantly, the victims of his crimes and others like them.
"`We hope for justice, but also that Ian will truly take responsibility for what he's done. We would urge any other victims to contact the authorities."
The message was signed by lead guitarist Lee Gaze, rhythm guitarist Mike Lewis, bass player Stuart Richardson, keyboard player Jamie Oliver and drummer Luke Johnson.
Watkins will be sentenced on December 18.
Meanwhile, the Independent Police Complaints Commission has announced that it is investigating how South Yorkshire Police handled allegations against Watkins made last year.
- PAA
