British mental health campaigner Jonny Benjamin MBE ran the marathon with the man who talked him down from a bridge during the "worst moment" of his life.
The 30-year-old and the "stranger on the bridge" Neil Laybourn completed the race together for the mental health charity Heads Together, founded by the Duke and Duchess of Cambridge, and Prince Harry.
They managed to raise £30,000 for the campaign, and finished the 26.2 mile marathon in five hours and twenty-eight minutes.
The pair are close friends after meeting in 2008 on Waterloo Bridge when Benjamin was prepared to jump off after being diagnosed with schizoaffective disorder - which is a cross between schizophrenia and bipolar.
Good samaritan Laybourn managed to talk Benjamin down off the bridge by promising him things "would get better" and showing his belief in Benjamin. After 25 minutes, the emergency services arrived and the two went their separate ways.
Eight years later, they were reunited after Benjamin tracked Laybourn down, which was turned into an award-winning documentary, shown on Channel 4 in 2015.
"I was in the worst place of my life and just thought it would never get better," Benjamin reflected to the BBC after his emotional reunion with Laybourn.
"I ran away from the hospital and I went to this bridge. I was on the edge and this stranger then appeared from nowhere and began talking to me. It sounds very simple but he said he believed in me and thought I would get better. That changed my mind about what I was about to do."
Prince William, Catherine and Prince Harry persuaded the pair to run the marathon for Heads Together.
Speaking prior to the marathon (via The Telegraph), Benjamin admitted: "Admittedly, I haven't done the training I needed for it.
"It's been a tough year so far with my relapse and going back into hospital, family illness, and most recently my Uncle and then Grandma passing away a few days ago. But I WILL complete the 26 miles! Even if I have to crawl some of the way!!
"This feels like such an important moment for mental health. They're calling this the world's first ever #mentalhealthmarathon. It's a privilege to be part of it."