Little-known jockey Padraig Beggy, who served a one-year drugs ban, won the Epsom Derby on Saturday on Aidan O'Brien's 40-1 shot Wings of Eagles.
It proved a debut Derby victory for 31-year-old Beggy, who was given the suspension in Australia in 2014 after a positive test for cocaine.
The outsider came from deep to beat much-fancied stablemate Cliffs of Moher and 7-2 favourite Cracksman.
"It's brilliant, I can't describe it," Beggy told BBC Radio 5 live.
He added: "I got into a bit of trouble in Australia and made a mistake. It is something that I've got to put behind me. I was knocked down then and had to pick myself up and come back fighting, and today I think I've proved that."
With only two horses behind him with three furlongs to run, Beggy led Wings of Eagles on a late charge to beat Cliffs Of Moher in the dying strides. Cracksman, ridden by Frankie Dettori, was third.
"I dreamed of it when I was fairly young. I had nearly given it up," added Beggy.
"Fair play to Aidan O'Brien - it doesn't matter what price you are riding when you are riding for Aidan in a big race."
The result had looked like going with the form book as Cliffs Of Moher (5-1) just got the better of the two Frankel colts, Cracksman and Eminent, inside the final furlong.
But that was not taking into account Wings Of Eagles - the son of 2011 Derby winner Pour Moi - who provided O'Brien with a sixth Derby winner.
"It means the world," added Beggy. "I'll go down in history because I've won the Derby."
It was Beggy's first run in the Derby and trainer O'Brien was full of praise for his jockey.
"He's a brilliant rider, a world-class rider," O'Brien told BBC Radio 5 live. "We're very lucky to have him."
BBC Sport horse racing correspondent Cornelius Lysaght
We said that any one of about 10 or 12 might win and though Wings Of Eagles was maybe quite low down that list, he was definitely on it after a promising second at Chester.
If one's honest, the presence of Paddy Beggy on board didn't gain the horse any extra followers because although he's doing well, he's seen as batting down the order for Team O'Brien.
But, along with the winner who swept by his rivals in great style, Beggy was star of this show, clearly delighted to win, but also immensely grateful to O'Brien who's supported him as he's rebuilt his career after the drugs ban.
There were barely one and a half lengths between the first four - there is probably no superstar there, but all four are good solid performers.