The 11-1 shot Numbersixvalverde won the Aintree Grand National from last year's winner and joint favourite Hedgehunter.
Niall Madden celebrates guiding his 11-1 shot to victory
Coming to the last, Hedgehunter looked set to become the first back-to-back winner since Red Rum.
But Numbersixvalverde, ridden by Niall 'Slippers' Madden and trained by Martin Brassil in County Kildare, pulled away to win by six lengths.
The other 5-1 joint favourite Clan Royal was given third in a photo-finish ahead of Nil Desperandum at 33-1.
Madden had kept his mount at the back of the field for the first circuit of the Liverpool track but they crept into the race on the second circuit.
After the leader Ballycassidy fell at Valentines - the 25th of 30 fences - it left the top two in the betting market, Hedgehunter and Clan Royal, at the head of the field.
Numbersixvalverde moved up to challenge and the trio pulled away from the rest of their rivals.
Madden and his mount pulled ahead over the last and although Ruby Walsh on Hedgehunter tried to respond, the gelding was carrying far more weight than last year and Madden managed to quicken over the long run-in for a six-length win.
"It's brilliant. I had a dream run the whole way round and he jumped super," said a jubilant Madden, who was making his debut in the Aintree Grand National.
"I wasn't sure I'd won until I crossed the line though. This means everything to me. It's magic.
"I've tried to imagine winning this race since I was a boy but I couldn't."
Winning trainer Brassil also could not believe his luck.
"It is unbelievable and it was like watching a movie out there. Niall gave him a great ride and never panicked - it is all hard to believe really," he said.
The race was delayed after a false start when Ross Comm went over the starting tape.
Only nine horses of the 40 starters finished, among them Nina Carberry on Forest Gunner, who was the last home.
Tyneandthyneagain, trained by Howard Johnson, fell at the first but got back up again, only to suffer a fatal injury when he came down at the 11th resulting in him having to be put down.
Jockey Stephen Craine had to be taken to hospital with a suspected broken collarbone when he came down on Ebony Light.
Winner Numbersixvalverde was napped by our man Honest Frank in the BBC Sport pinstickers' guide.
He had also successfully tipped War of Attrition (15-2) for last month's Cheltenham Gold Cup.
1615 John Smith's Grand National Chase (4m 4f)
1. Numbersixvalverde (N P Madden) 11-1
2. Hedgehunter (R Walsh) 5-1 Jt Fav
3. Clan Royal (A P McCoy) 5-1 Jt Fav
4. Nil Desperandum (T P Treacy) 33-1
40 ran. Dist: 6, 1¼