OMG how upsetting.
I just found out about this an hour ago.
He didn't seem quite right when I saw him on Loose Women several years ago, when he went on to talk about his battle with his mental health, and his financial issues. He seemed subdued and low.
No idea what he has died of as it's inconclusive at the moment... 
I went to a couple of S Club 7 concerts circa 2000 to 2002, (with the kids when they were little,) and they were sooo good, and this has really shaken me. And DH, and my (now adult) children too.
R.I.P. Paul Cattermole. โค