Henllan Harri caused a 40-1 upset when he just held on from Vyta Du Roc in a thrilling finish to the bet365 Gold Cup at Sandown.
The nine-year-old, trained by Peter Bowen and ridden by his son, Sean, made most of the running and kept all-comers at bay as he captured the last big steeplechase of the season.
Henllan Harri was 4lb wrong at the weights but that did not stop him from landing the spoils for the Pembrokeshire stable.
The pack closed in up the final hill, but Henllan Harri got the verdict by a head from the Nicky Henderson-trained Vyta Du Roc (6-1), with Colin Tizzard's Theatre Guide (20-1) just a neck away third.
The winning rider said: "I thought I had (won) but then Daryl (Jacob, on Vyta Du Roc) said he'd won it.
"He held on well and battled on very hard. He did what he does best. He stuck on well all the way and stayed every yard.
"He's very tough."
Apple's Jade ran out a wide-margin winner of the Irish Stallion Farms EBF Mares Champion Hurdle at Punchestown.