Standing on the start line of this year's London Marathon, 23 year-old Josh Griffiths, of Gorslas, was hoping to run a time fast enough to earn his spot in the Wales team for the 2018 Commonwealth Games.

What happened over the next two hours, 14 minutes and 49 seconds saw the Swansea Harriers club runner produce the run of his life, to finish the fastest Briton in the entire race.

Josh, a virtual unknown prior to the race, shot to instant fame on crossing the finish line. Not only had he fulfilled his pre-race aspirations, his time was also good enough to secure his place in the Great Britain squad for this summer's World Athletics Championships in London.

The S4C cameras have been granted exclusive access to film Josh as he prepares to line up against the world's best marathon runners in the event in London on Sunday, August 6

Ahead of the big day, the former Ysgol Dyffryn Aman said: “I was hoping to run a Commonwealth Games qualifying time of 2 hours 16 minutes, but that was going to be a long shot. I'd need the best race I'd ever run to do it.

“But to come away with 2 hours 14 minutes and qualify for the World Championships really exceeded what I thought I could do.

It was the fastest time by a Welshman in 21 years, but even in the late stages Josh was conscious of just keeping going and not taking anything for granted until he crossed the line.

“As soon as I crossed the line I was thrust into another world completely. People wanted to hear my story whereas going into the race no one, apart from my family and friends, knew I was running, said the Sports Coaching student.

“I've started to get used to it now and got back to training properly. I've not let it affect me too much.”

“I'm aware I'm going to a World Championships, so I have to up my game a little. I guess the main difference for me is seeing myself as a professional runner rather than a student who runs.

“It's more of a mental change than anything. I think of myself now as an athlete rather than anything else. I've earned my place on the start line, just like everyone else and I'll just try and enjoy having the home crowd behind me.”

Josh Griffiths: Mr Marathon is being broadcast on S4C at 9.30pm on August 3.