Aidan O'Brien's staying star regained his Ascot Gold Cup crown when battling on bravely to get the better of Trawlerman in the closing stages.
The Aidan O'Brien-trained six-year-old stayed on powerfully to land the prize by half a length from Mojo Star in a season that saw him go unbeaten in six starts two years ago, but injury caused the son of Galileo to miss his defence last campaign.
Ballydoyle's staying star was restricted to just two runs last season, filling the runner-up spot on both occasions, including when denied a neck by Trawlerman in the Long Distance Cup.
Victories at Navan and Leopardstown this season saw Kyprios sent off the well-backed 11/10 market leader to regain his Gold Cup crown and following a prolonged battle with his Long Distance Cup conqueror Trawlerman, Aidan O'Brien's five-year-old would edge home in front.
William Buick ensured the fractions were solid on the front-running Trawlerman, but Ryan Moore always looked well-positioned on Aidan O'Brien's contender, tracking the keen-going Benoit De La Sayette-ridden Caius Chorister in third for much of the two-mile four-furlong prize.
The tempo lifted as the field of nine turned for home and Ryan Moore kicked his mount to the front with a furlong to travel. William Buick did his best to galvanise Trawlerman down towards the rail, but the Aidan O'Brien-trained Kyprios always looked to be finding plenty out in front and went on to claim Group 1 honours by a length.
Trawlerman's stablemate Sweet William ran on to grab the third spot, but he was no match for the front pair, who pulled five lengths clear of their rivals.
Willie Mullins' high-class dual-purpose horse Vauban briefly looked to lay down a challenge but ultimately faded out of contention back in fourth.
The victory meant Kyprios became the first horse since Kayf Tara in 2000 to regain the Gold Cup and the third horse ever to do so.
"It was smooth early, that's where I wanted to be and then the filly (Caius Chorister) ran off with Benoit (De La Sayette) and I was having to go round her. He started travelling a bit too well too early again and I got there going very easy," explained Moore, who was riding his 82nd Royal Ascot winner after surpassing Frankie Dettori's record on Port Fairy in the Ribblesdale Stakes.
"I said to Aidan that he's the class horse in the race and he stays the best, so I've just got to get it right. I didn't get it quite right, but he still won.
"He's an unbelievable horse. Aidan knows exactly what they need to do, he knows how to get them here better than anyone.
"It's lovely to ride a horse like this."
It was a record-extending ninth Gold Cup triumph for O'Brien, who said: "Ryan gave him an incredible ride, I'm delighted. There are incredible people around him and he's an incredible horse.
"It wasn't easy because he passed the second horse here last year (Champions Day) and he came back at him, I could see Ryan biding his time. It was incredible really, it's masterful stuff, really.
"It's not simple but this is an incredible horse, I'm delighted for everybody really.
"Ryan is a master, and it was a genius ride. I could see what he was at, he wanted to be handy as he thought the pace was slow.
"He had to sit back a little as he didn't want to get there too early, it's tricky, it's a fine balancing act the whole time but it was masterful."
