Scudamore said: "For the first time in my life I'm pretty speechless. It's wonderful - I thought he'd win, but I never imagined he'd do it as easy as that.
"He's a phenomenal racehorse, he's a pleasure to ride and a great credit to everyone. To win a King George on his fourth run over fences, it just shows the hard work everyone back at the yard has done and I'm so thrilled to be part of it."
He added: "Between myself, my father (Peter) and grandfather (Michael) we've had about 33,000 winners and he's the best one of the lot."
Connections of Thistlecrack kept punters guessing for a while as to which Kempton race he would contest, with the Kauto Star Novices' Chase an apparently easier option.
On the decision to go for King George glory, part-owner Heather Snook said: "It wasn't that hard actually, because he had to take on the big boys sooner rather than later. Tom was happy, we were happy and Colin was happy, so we let him take his chance. We're very lucky people."
Tizzard revealed the decision on his festive target had been made some time ago.
"As soon as I made the entry we knew which way we were going to go, although we sort of pretended we didn't," said the Dorset-based trainer.
"He's not a five or six-year-old, he is eight and he'll be nine in a few days' time. He's at the peak of his powers and he's just proved we all got it right."
Reflecting on the mesmerising display, he added: "It's quite frightening to watch, isn't it? When Cue Card went up beside Thistlecrack six or eight (fences) out, I thought 'goodness me'. It's a very fickle world we live in.
"We've all seen Thistlecrack for the last few years, he's had his biggest test and he's a brilliant horse."
