The Someone You Loved singer was on a stroll with his friends in Hampstead Heath when they saw the woman on the ground.
Witnesses told The Sun of how he came to the elderly ladies rescue, immediately dialled 999, and staying by the woman’s side until help arrived.
Shortly afterwards, an ambulance arrived and transported the injured party to hospital, with Lewis only leaving once he had confirmation she was safe.
An onlooker said: “Lewis is not just a superstar but a superhero. We saw him helping an old woman who had collapsed on the ground and it turned out he’d rushed over to help when he saw her.
“Lewis and his mates called an ambulance and made sure they stayed with the woman until help arrived. He clearly has a massive heart. Good on him.”
The Before You Go singer has been spending time at his home in London following the news that he would be taking a break from performing.
Lewis was diagnosed with Tourette’s last year and was forced to cut his performance short at Glastonbury festival in June because he was struggling.
“The fact that this probably won’t come as a surprise doesn’t make it any easier to write, but I’m very sorry to let you know I’m going to be taking a break from touring for the foreseeable future. I used to be able to enjoy every second of shows like his and I’d hoped three weeks away would sort me out.
“But the truth is I’m still learning to adjust to the impact of my Tourette’s. On Saturday it became obvious that I need to spend much more time getting my mental and physical health in order, so I can keep doing everything I love for a long time to come,” the singer wrote in a statement.
At Worthy Farm, Lewis struggled during a set with his twitches on stage and told fans in attendance that he was finding it hard.
He has also been transparent about his health struggles in his Netflix documentary, Lewis Capaldi: How I Am Feeling Now, earlier this year.
In the docs-film, the Glasgow native admitted he suffered from anxiety and hypochondria – a condition which sees causes additional worry about health.
Since he confirmed he would be taking a break, Lewis has been seen out and about in London and was seen watching Charlton Athletic take on Aberdeen in July.
Related: Fans convinced Arctic Monkeys have just played their final show ever
