Galopin Des Champs was sent off the 7/5 favourite to make a successful step up in trip in the three-mile-two-furlong showpiece under Paul Townend.
And while he was unproven over the distance, his stamina was never in doubt as he outstayed Bravemansgame up the Cheltenham hill to claim an impressive seven-length verdict.
Conflated claimed third at 22/1, with Noble Yeats wrapping up the places in fourth.
Previous race winners Minella Indo and A Plus Tard lined up again, but neither ever looked like landing a real blow and were pulled up, while Ahoy Senor fell after setting out to make all, bringing down Sounds Russian in the process.
Hewick was also crashed out at the last, but all three horses were soon on their feet again.
Townend told ITV Racing: "It wasn't plain sailing, that's for sure. Everywhere I went there was a bit of trouble, his jumping just got a bit careful for the first circuit but going out I had full faith in him that he was going to get me out of trouble and he did.
"He's a proper, proper horse because he's run about three different races and still won a Gold Cup.
"I could see them all going at it in front of me and it allowed me to fill up and be the last one on the scene. If they'd have sat in front of me and quickened, I'd have had to chase them but it just gave me a chance to fill him up after making up a lot of ground.
"This is race is just different."
Owner Audrey Turley added: "It's like a dream come true. It's something I never dreamt of, I never thought we would be here with such a wonderful horse as Galopin Des Champs. Really and truly, myself, my daughter Sarah and my husband, we're just so thrilled.
"We've huge support here, all our family are here, so the excitement has been high all week. Well actually, for much longer than that.
"I don't know what to say! It's just so unbelievable and wonderful. Really we just have to thank magnificent Willie Mullins and all the team at Closutton, we wouldn't be here having this wonderful day without them.
"We're going to forget all that (last year, when the horse fell at the last fence), these things happen and in racing anything can happen as we know. Here we are, beautiful sunshine and Galopin has won - we're thrilled."