Bryony Frost became the first female jockey to win the King George VI Chase, riding Frodon to victory at Kempton.
The 20-1 chance led throughout the three-mile race and held off the fast-finishing Waiting Patiently (12-1), ridden by Brian Hughes, to give trainer Paul Nicholls his 12th King George win.
Hat-trick-chasing Clan Des Obeaux, the 85-40 favourite, was back in third.
"I have had the absolute best time going round there on him," said a delighted Frost, from Devon.
"He has just smashed everyone's expectations. I don't argue with him too much as he is his own personality.
"I cannot stress how much this horse means to me - he is my life. You dream as a little girl to ride a horse like this."
The win gave Frost her 175th career win, making her become the most successful female National Hunt jockey of all-time.
Frost and Frodon had also made history at the 2019 Cheltenham Festival, winning the Grade One Ryanair Chase.
This time, in front of deserted stands at the Surrey track, Frodon was in front by the first fence, allowing Frost to dictate the pace.
Her rivals were never able to get past her and some solid jumping on the home straight maintained the momentum.
Nicholls was surprised that his 12th win in the traditional Boxing Day showpiece had come with the outsider of his four runners.
"It's amazing - although obviously he's a very good horse on his day," he said.
"He loves it round here, and I said to Bryony: 'Just go as quick as you can, keep galloping and sail on - you know he's tough and brave.'
"You've just seen today what a remarkable horse he is. He never knows when he's beaten."
Earlier, Silver Streak beat Epatante, this year's Champion Hurdle winner, to take the Christmas Hurdle.
Epatante had gone off as the 1-5 favourite but Silver Streak and jockey Adam Wedge put in a superb display of jumping.
An error at the third-last did not help Epitante and jockey Aidan Coleman and although they tried to rally, Silver Streak went away again to win by six and a half lengths.
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