The 12-1 chance Al Boum Photo, ridden by Paul Townend, put in a superb display to give trainer Willie Mullins a first Cheltenham Gold Cup victory.
Mullins, the Festival’s most successful trainer, had previously finished second six times in the prestigious race.
Al Boum Photo had some anxious moments with his jumping. but raced away to win by two-and-a-half lengths.
Fellow Irish challenger Anibale Fly (22-1) was second with the grey Bristol De Mai (18-1) back in third.
“I can’t believe it,” an emotional Townend told BBC Radio 5 Live. “It means everything. It’s the pinnacle and I can’t believe I’ve won it.
“I got in a beautiful rhythm. When you’re going well, it just seems so simple.”
For a long time it looked like last year’s winner Native River and runner-up Might Bite would be in the shake-up again as they headed the field after the first circuit.
Clan Des Obeaux, part-owned by former Manchester United manager Sir Alex Ferguson, looked like he would challenge.
But it was Al Boum Photo, one of four Mullins runners in the race and the only one to make it into the second circuit, who started to look the strongest.
The pair had a slight wobble at the second last before safely negotiating the final fence and battling up the famous Cheltenham hill for the victory.
Townend and Al Boum Photo had been at the centre of a dramatic incident at last year’s Punchestown Festival that left the jockey with a 21-day ban for dangerous riding.
Townend, while leading the Champion Novices’ Chase, steered the horse right of the final obstacle having apparently heard a shout telling him to bypass it.
In the process he collided with fellow runner Finian’s Oscar and crashed into the white fence.
More to follow.