The former Great Britain full-back retired from playing on Tuesday, after a career in which he played 495 senior games and scored over 1000 points.
While he would very much have liked to have carried on, the hip injury he has been carrying was simply too much for his 35-year-old body to handle any more.
“Obivously it was a very difficult call to make,” he said.
“With the injury the way it is now, it’s ultimately the right decision.
“I’m going to need some substantial surgery doing now on the hip, which will give me back the quality of life I’ve not had for a good few months.
“It’s been a huge privilege for me to represent this club for so long.
“That’s what makes the decision even harder, but it’s one of those things.
“My playing career was never going to last forever, and it’s ultimately the right call.”
Wellens has been unable to participate in a number of ordinary activities whilst injured, something he could no longer tolerate.
“The simple things in life that you take for granted I’ve not been able to do in recent months,” he explained.
“Like have a kickabout in the garden with my son.
“It’s got to the point where the injury is that debilitating that I’m in constant pain at the moment.
“I need to get that sorted. I’ve exhausted every avenue possible in trying to get back fit.”
The veteran remains incredibly proud of his long career at Saints, though, and he never imagined as a youngster that he would go on to occupy a position in the club’s pantheon of great players.
“What I’ve got to do now is look at the big picture,” he said.
“I came into the club as a 16-year-old playing for the juniors, and now I’m a 35-year-old man with three children and my wife, and I’ve enjoyed so many successful times in that period, and built so many great relationships.
“If you’d offered me even half of that when I started I’d have bitten your hand off.
“So I am extremely proud of my achievements in my time here at the club.”