TORFAEN council's leader Brian Smith is to retire in the summer after 20 years at the top - after warnings from his doctors.
The Labour councillor, who has represented Fairwater for the last 34 years, will not apply for re-election.
Councillor Smith had an operation to remove a large brain tumour in July and, though the surgery was successful, has been advised that he should resign to preserve his health.
He will remain as leader until the local government elections on June 10.
The 63-year-old councillor, who was born and grew up in Old Cwmbran, said: "I was planning to do one more term but the doctors and specialists were saying I couldn't sustain it if I wanted to stay alive.
"I regret having to retire but everyone's been putting the pressure on me, including my own GP. When I was fit I could cope with it but I can't now. I think my record of 34 years as the ward's representative and 20 years as Leader speaks for itself.
"But one door closes and another one opens, and I've come to terms with thinking I'm going to be just Mr Smith."
Councillor Doug Davies, Mayor of Torfaen, said: "We're all very sorry to see Brian has decided to resign.
"Brian could speak for an hour or more on a subject without referring to notes and there are not many politicians who could do that.
"He's been our leader for the last 20 years and I'm sure all the members of all parties are sorry to see this."
Councillor John Taylor said: "Brian has told us that he is going to retire at the end of this council.
"Members are aware of that and he has given his notice.
"He has served as leader for a long time and has taken us through a lot of change very successfully.
"I'm sorry to see him go. He's been very skilful in being able to lead the council through difficult decisions and move us forward.
"It will be up to the new council to decide on a new leader so we can't make any kind of judgment until after the elections."
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