Minella Indo won a thrilling Cheltenham Gold Cup under Jack Kennedy to deny Rachael Blackmore aboard A Plus Tard in a 1-2 for trainer Henry de Bromhead.
Victory sealed a historic hat-trick for the Irish trainer, who also landed the Champion Hurdle and Champion Chase.
The 9-1 chance Minella Indo won by one and a quarter lengths with two-time champion Al Boum Photo in third.
Blackmore - top 2021 Cheltenham rider with six wins - was hoping to become the first female jockey to triumph.
Picking A Plus Tard ahead of Minella Indo was probably trailblazing Blackmore's only wrong decision of the week, but it was an emotional success for Kennedy.
"I can't believe it. This is what I have dreamed of as a child," said the 21-year-old rider, who has already broken his leg four times in his short career.
"It could always be a lot worse - broken legs and broken collarbones will heal. It's obviously unfortunate, but you have to get on with it.
"It's definitely the best day of my life. I know I'm still young, but I suppose I have been in the position where I could have been winning them for a couple of years, so to get it done is brilliant."
Delighted De Bromhead, who won Wednesday's Queen Mother Champion Chase with Put The Kettle On, was left to take in what he had achieved.
"It's all come together here and it's fantastic," said the 48-year-old, who trains in Knockeen, County Waterford,
"To win a Cheltenham Gold Cup is something you dream about. I think I'm still in my hotel, it's Monday evening and I'm about wake up and nothing's even started yet. That's where I'm at at the moment, it's brilliant."
The 2018 winner Native River was fourth and long-time leader Frodon fifth, while last year's RSA Chase victor Champ and 2020 Gold Cup runner-up Santini were pulled up.
Blackmore was given a two-day suspension for "using her whip above the permitted level from turning in".
How the race unfolded
Twelve runners went to post, and Bryony Frost led from the front on the six-time Cheltenham winner Frodon.
The 2019 and 2020 victor Al Boum Photo was one of several travelling smoothly, along with his Willie Mullins-trained stablemate Kemboy, as the race developed.
Blackmore, who was the first female jockey to win the Champion Hurdle after victory with Honeysuckle on Tuesday, was another going well on A Plus Tard.
Frodon began to fade two fences from home and Minella Indo, second to Champ at Cheltenham last year, hit the front and could not be caught up the hill.
'A great talent who deserves this' - reaction
Katie Walsh, Cheltenham Festival-winning jockey on BBC Radio 5 Live
Jack Kennedy is a fantastic jockey and has been riding out of his skin.
He has had some horrible injuries over the years but is a great Irish talent and really deserves this.
Everyone felt Rachael went for the right horse in A Plus Tard but Minella Indo operates well around here.
More success for Ireland
The final day of the 2021 Festival followed the pattern of the previous three days with Irish horses dominating.
As well as Minella Indo, there were five other Irish-trained victories to leave Ireland 23-5 winners over Great Britain in the battle for the Prestbury Cup.
Only the Will Biddick-trained Porlock Boy (16-1) in the Festival Challenge Cup Open Hunters' Chase could deny the Irish on another day of success.
Blackmore's sixth win of the Festival came on the 2-1 chance Quilixios, trained by De Bromhead, in the Triumph Hurdle.
But De Bromhead missed out on the leading trainer's trophy after Mullins claimed a double in the last two races to win on countback.
Colreevy (9-4) edged out stablemate Elimay to win the inaugural Mares' Chase before Galopin Des Champs (8-1) claimed the Martin Pipe Conditional Jockeys' Handicap Hurdle.
Earlier, Belfast Banter gave Kildare-based trainer Peter Fahey and jockey Kevin Sexton a first Festival win when the 33-1 shot won the County Hurdle.
And Mark Walsh took advantage of the absence of Jonathan Moore to pick up a spare ride on Vanillier (14-1) and the pair made all the running in the Albert Bartlett Novices' Hurdle, giving trainer Gavin Cromwell a second win of the week.
Moore had missed out on the ride on Stayers' Hurdle winner Flooring Porter on Thursday and he was not fit enough to ride on Friday.
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