The former medical director at the Princess Alexandra Hospital in Harlow has died of coronavirus.
Nigerian-born Dr Alfa Saadu retired following a glittering 40-year medical career in 2017, but carried on working part-time at the Queen Victoria Memorial Hospital in Welwyn, Hertfordshire.
In a social media post, his son Dani said he'd been fighting the virus for two weeks but "couldn't fight anymore."
Dr Saadu died on Tuesday morning at the age of 68.
"He was a very passionate man, who cared about saving people. As soon as you spoke to him about medicine his face would light up," Dani told ITV News Anglia.
"My dad retired and was working part-time at the Queen Victoria Memorial Hospital in Welwyn, Hertfordshire until his passing. He was a massive family man and we did everything together. Family came first. He left two sons and a wife, who is a retired Doctor herself in Occupational Health."
Dani also confirmed to ITV News Anglia that his dad was not working on the frontline against coronavirus, and hadn't specifically come out of retirement to help the NHS deal with the pandemic.
Dani also pleaded with people to "take coronavirus seriously and listen to the government" and added that the virus "is not a joke."
The Chief Executive at Princess Alexandra Hospital, Lance McCarthy, said in a statement that Dr Saadu will be "remembered fondly by many."
"Alfa was well-known at the trust for his passion for ensuring our patients received high quality care," he said.
"He was a committed member of the team and is remembered fondly by many. His family and friends are in our thoughts at this sad time.”
A spokesperson for Hertfordshire Community NHS Trust added: “We are very sorry to learn of the death of Dr Alfa Saadu. Our thoughts are with his family and friends. Dr Saadu had most recently worked at the Queen Victoria Memorial Hospital in Welwyn. He was held in high regard by everyone he worked with.”
The former President of the Nigerian Senate, Bukola Saraki, was among those to pay tribute to Dr Saadu in his home country.