A record-breaking veteran climber fell 600-feet to his death off a steep Mexico mountain after failing to tie a knot in his rappel rope.

Brad Gobright, 31, had been rappelling down El Sendero Luminoso at El Potrero Chico on Wednesday with climbing partner Aiden Jacobson, 26.

Gobright and Jacobson met each other for the first time on the day of the climb. The night before, the veteran climber had posted to Instagram asking whether anyone wanted to join him. Jacobson, from Phoenix, answered the post, and the pair met up the next morning.

The pair used a 260ft rope to simul-rappel down the side of the mountain after they reached the peak, according to Outside. The climbing technique is where two climbers, using opposite ends of the same rope, descend down the side of a mountain. The rope is rigged to an anchor, and each climber acts as a counterweight to the other. If one stops weighting the rope, it could cause the other to fall.

In this case, Gobright and Jacobson did not tie potentially life-saving stopper knots in the ends of their ropes because it could cause the ropes to get stuck, according to Outside.

As the pair descended, they misjudged the length of rope they had on either side - with Gobright having less than he thought. And as they hadn't tied knots into the rope, when it reached its end it slipped out of his rappel device, causing him to fall 600-feet.

Jacobson fell at the same time, but his fall was broken by bush and he injured his ankle.

Brad Gobright, 31, (pictured) was semi-rappelling on Wednesday in Mexico with Aiden Jacobson, 26, who rappelled of an 80-meter rope, causing Gobright to fall too

Aiden Jacobson, 26, (left) met Gobright on the same day of the climb. He suffered a broken ankle during the fall

The pair descended the 2,500-foot mountain, but misjudged the length of rope they had on either side - with Gobright having less than he thought. And as they hadn't tied knots into the rope, when it reached its end it slipped out of his rappel device, causing him to fall 600-feet

Jacobson, who had five years of climbing experience, posted this image of El Potrero Chico just days before the fatal climb

Jacobson told Outdoor that before the fatal fall they had reached an anchor at pitch nine, they opted to go down to pitch six, just 50 feet above the ledge.

The rope at that point was slack, and the climbers did not pull it to its midpoint. At that stage, Gobright's side of the rope was tangled in bush to the side, and Jacobson's was touching the ledge.

Jacobson told Outdoor: 'I asked if we were good and he said "yes, we can untangle the rope on the way down. We didn't tie knots in them either ... I was a bit above him. I was on the left. He was on the right. Then all of a sudden I felt a pop and we started dropping.'

The climbers were about 30 feet above pitch five when they fell at the same time. There had been less rope on Gobright's side than the pair initially thought, and because there were no knots in the end of the rope, it caused him to slip.

'It was basically a blur. I screamed, he screamed. I went through some vegetation, and then all I remember is seeing is his blue Gramicci shirt bounce over the edge,' Jacobson told the publication.

Costa Rican climber, Gino Negrinni, who was on the mountain at the time said he saw the climbers and then later heard their screams.

In October 2017, Gobright set a speed record for ascending the Nose route of El Capitan in Yosemite National Park, one of the world's most technical and dangerous verticals

El Sendero Luminoso at El Potrero Chico in Mexico reaches a whopping 1,500ft

Gobright had been climbing since he was seven and in 2017 set a speed record for ascending the difficult Nose route of El Capitan in Yosemite National Park

Negrinni said he and his climbing partner saw the two drop to the fifth pitch and went down to help Jacobson.

The rope was also on the fifth pitch but Gobright was not and it was assumed he continued falling down to an area known as the Skull Ampitheatre.

Gobright had landed in Mexico a few days before and was collected from the airport by Joel Heriberto Guadarrama Garcia. Who received details of the accident from Negrinni.

'I arrived with Brad in Potrero at 3:40 in the afternoon and Brad just dropped his bag, and fifteen minutes later went and free soloed Yankee Clipper,' Garcia told Rock & Ice.

Gobright had been climbing since he was seven years old and is one of the few who have climbed the Salathé Wall free in a single day.

In June 2015 he made the first free ascent of The Heart Route with Mason Earle.

With Scott Bennett he climbed Zodiac, The Nose and Lurking Fear in less than 24 hours in 2016.

In October 2017 he set a speed record for ascending the Nose route of El Capitan in Yosemite National Park, one of the world's most technical and dangerous verticals.

Gobright and climbing partner Jim Reynolds raced up the nearly 90-degree, 2,900-foot precipice in just two hours and 19 minutes.

Alex Honnold - the only person to free solo El Capitan - said he was 'sad' and the climbing world lost a true light'

Gobright and climbing partner Jim Reynolds (left) raced up the nearly 90-degree, 2,900-foot precipice of El Capitan in just two hours and 19 minutes

The pair, from California, broke the previous record set in 2012 by four minutes. That record was set by Alex Honnold - the only person to free solo El Capitan.

Honnold said he was 'sad' and the climbing world lost a 'true light'.

He posted an Instagram tribute to Gobright, calling him a 'warm, kind soul - one of a handful of partners that I always loved spending a day with'.

'I suppose there’s something to be said about being safe out there and the inherent risks in climbing but I don’t really care about that right now,' Honnold continued.

'I’m just sad for Brad and his family. And for all of us who were so positively affected by his life. So crushing. Brad was a real gem of a man. For all his strengths and weaknesses (like his insanely strong fingers, or living out of a Honda Civic...) at the core he was just a good guy.'

Emily Harrington was climbing with Alex Honnold on El Capitan on Sunday. She fell but was harnessed into ropes so escaped with some scratches and cuts.

Gobright spoke about safety after he beat Honnold's record.

'The big thing that Jim and I were worried about was that to some extent you have to kind of put safety behind you when you're trying to move that fast,' Gobright said.

'It requires a lot of focus, much more than a regular climb. Speed climbing requires your full attention.'

Gobright previously said about climbing El Capitan in record time: 'To some extent you have to kind of put safety behind you when you're trying to move that fast'

In the spring Gobright completed free ascents of The Shaft, El Niño Pineapple Express and Golden Gate in just one day

More than two dozen people had been killed on El Capitan since 1905. According to Ken Yager, the president and founder of the Yosemite Climbing Association, it typically takes three days to complete the ascent, which sits 7,569 feet above sea level.

Conditions were not ideal, with smoky air and the route crowded with climbers, according to Gobright.

To maximize their speed, the pair ditched camming devices meant to prevent falls and whatever weighty gear they could live without. They didn't pack food or water.

About two hours in, Gobright said he could feel the smoke affecting his breathing. His throat was scratchy and his mouth was dry.

Gobright said that when he and his partner reached the top, their family and friends were cheering them from the ground below. Five minutes later he received a text message from the previous record holder, Hans Florine. He was sending his congratulations.

Florine and Alex Honnold climbed the Nose route in two hours and 23 minutes in June 2012. Florine has set eight speed records for his climbs up the Nose since 1990.

Gobright said he finally realized he could be a contender for the speed record when and Reynolds climbed the nose a year and a half ago.

'Before Jim and I were trying to go for the record, we'd just do it fast so we'd have time to do more climbs before the sun went down,' he said.

'Thinking we could try for the record seemed crazy at first. It was this really big, big goal that seemed kind of out of reach. I think that's why we wanted to do it.'

Last year they did the Yosemite Triple - Mt Watkins, El Cap and Half Dome - in a day.

In the spring Gobright completed free ascents of The Shaft, El Niño Pineapple Express and Golden Gate in just one day.