The Saints finished as runners-up from 2007 to 2011, but put that run behind them with a 14-6 victory over Wigan Warriors at Old Trafford yesterday evening.
Wellens told Sky Sports News: "I've told a fair few lies in press conferences this week about those five years not bothering me but it has absolutely haunted me.
"I've also got to say that this one's for our supporters. They've lined the terraces here year on year, for five years and we've gone and lost. They've suffered like the rest of us so that's for them tonight
"The first half, especially in the first 30 minutes we shot ourselves in the foot. We went back to basics in the second half and now we're the champions. All that adversity makes it all the more sweeter. We've had our ups and downs, but that's it now we're the champions."
The title is St Helens' first since 2006.