Frost had led Frodo to three wins earlier
Jockey Bryony Frost wrote the history of the Cheltenham Festival by becoming the first woman to win top-level victories by jumping to the meeting, when Frodon won an emotional triumph in the Ryanair Chase.
Frost, 23, the daughter of Jimmy, the big winner of the national competition, took off after a victorious victory over a 9-2 chance, coached by Paul Nicholls.
"He's Pegasus," Frost said in tears after his bold mount finished in front of Aso and Road To Respect.
While the jockey and his horse returned to an enthusiastic reception in the winner's compound, Nicholls, ten-time champion of training, said it was "one of the best days of all time ".
Aso (33-1) stayed second, followed by Road to Respect (9-2) third.
Frost follows the path of Katie Walsh, now retired, who won a freshman race at the Festival last year when Relegate came first to Champion Bumper, a flat race governed by Hunt's national rules.
"We climbed a mountain to get there," Frost told BBC Radio 5 Live. "It's amazing and I'm going to enjoy every minute."
"He deserves all five, pat and carrots" – Frost for his privileged partnership with Frodo
Frost and Frodon have built a perfect partnership over the last two seasons, and their pace has taken hold at the front, right from the start of the race, over two miles and five stadiums.
The seven-year-old gelding was considered for the longest Cheltenham Gold Cup on Friday, but it was felt he would be better suited to this competition on a rain-softened course and he loved the trip.
Sub-Lieutenant and Road to Respect competed for first place, but there were only 33 outsiders, Aso, ridden by Charlie Deutsch for coach Venetia Williams, who could stay with the leader before having to settle for second place.
Frost, who earned his second win in Grade 1 after his victory in the Kauto Star Novices 2017 Kempton pursuit on Black Corton, said: "He's the most incredible fighter!
"He traveled, my God, he jumped, and by the time he was passed by two, most of the horses quit smoking.He caught me by the hands and said: do not be daring to give up, he is incredible.
"He deserves every high high, pat and carrot."
Frost at the forefront of the new race generation
Frost is from Buckfastleigh in South Devon
Frost is part of the new generation of female jockeys who stand out in a sport where women often compete with men on a level playing field.
On Tuesday, Rachael Blackmore, who wants to become Ireland's first Olympic champion in a title race that ends in April, won her first success at the Festival.
It was Frost's second win at the headliners meeting after winning the Foxhunter Chase on Pacha Du Polder in 2017.
She bounced back after suffering serious injuries during a fall last year, which ruled her out for three months.
In pre-festival column for BBC Sport, she described her partnership with Frodon, a Cheltenham specialist who has won five victories on the Gloucestershire circuit.
"He's numb with courage, he's more competitive and braver than me, he wants him, he knows his races and his courses very well," Frost said.
"If he was a kid going to school, he would definitely come out with A stars.
"When he was younger, he was quite optimistic and knew everything.This year, we really clicked, we just found this wave on which we ride together.
"I know for a fact that he's going to offer me 100% of himself and I'm going to give it back to him immediately." Frod "is the man." a privilege to be with him. "