Olympic champion triathlete Brownlee stops racing to help stricken brother (VIDEO)
With just 700 meters to go and closing in on victory at the World Triathlon Series, 26-year-old Jonny began to succumb to the hot and humid conditions in Cozumel, becoming dazed, disoriented and unable to control his legs as he stumbled toward race stewards.
Alistair, 28, quickly caught up with his brother, propping him up for the final part of the race and running with him over the finish line to ensure his second place finish.
In the midst of the incident, South African Henri Schoeman overtook the pair to claim victory, but his achievement was well and truly overshadowed by Alistair's noble gesture.
"If he'd conked out before the finish line and there wasn't medical support it could have been really dangerous," the elder Brownlee said.
"It was a natural human reaction to my brother but for anyone I would have done the same thing. I think it's as close to death as you can be in sport."
Following the race, Jonny was sent to hospital as a precaution after receiving medical attention at the finish line.
He later took to social media to thank his brother.
Jonny had needed to win the final race of the World Triathlon Series and see Spain’s Mario Mola finish no higher than fourth to be crowned world champion. All seemed to be going to plan for the Brit before the heat began to take its toll and he started to weave across the course.
With the younger Brownlee finishing second and Mola coming home in fifth, it was the Spaniard who took the title by just four points.
Despite his heroics, Alistair has competed fiercely with Jonny for the majority of their lives.
Both brothers excelled in sports at school and took up the triathlon after their parents encouraged their passion for the outdoors with hikes and bike rides in their native English county of Yorkshire.
Alistair began training for triathlons aged just 11 and was quickly followed into the punishing sport by his brother.
They tackle marathon swims at their local swimming pool, often followed by 50-mile bike rides through the Yorkshire Dales.
Alistair is the only athlete to win two Olympic titles in the event. He is also a two-time Triathlon World Champion, a two-time World Team Champion, a three-time European Champion and has won one Commonwealth title.
Jonny is the 2012 Triathlon World Champion and won the bronze medal in the Olympic triathlon at the London 2012 Games.
He also claimed the Olympic silver medal behind his brother at the Rio 2016 Games.
The act was reminiscent of when British sprinter Derek Redmond was helped over the finish line by his father after receiving an injury in his 400m semifinal at the Barcelona 1992 Summer Olympics.
Reigning world champion Redmond tore his hamstring halfway around the track, prompting dad Jim to enter the field to help his distraught, sobbing son over the line. Both received a standing ovation from the 65,000 fans.