(CNN) The main auction ring at Tattersalls, Europe's leading bloodstock auctioneers, is packed as Lot 325 nervously enters.
The yearling pricks up his ears as he walks next to his groom in the auction ring in Newmarket, the home of British racing.
After a frenzied bidding war, the colt is eventually snapped up by David Redvers, the British racing and bloodstock manager to the young Qatari Sheikh Fahad al-Thani and his brothers, for 3.5 million guineas ($4.8 million).
Bred by Madeleine Lloyd Webber, the wife of British composer Andrew Lloyd Webber, the colt is the world's most expensive yearling sold in the world this year.
Why are buyers willing to bet so big on untrained racehorses that are only between one and two years old and have yet to prove themselves on a race track?
The answer lies in the horse's bloodline.
Lot 325's father is Dubawi, Britain's most expensive stallion who commands a stud fee of £250,000 ($329,356), and has produced 37 Group 1 winners so far.
Owned by Goldolphin, the racing stables of Dubai ruler Sheikh Mohammed bin Rashid Al Maktoum, the Irish bred Dubawi is one of three super studs that currently dominate the world of racing.
The other two are Galileo and his unbeaten son Frankel, and their earning power rivals that of soccer stars Cristiano Ronaldo and Lionel Messi, and multiple grand slam tennis champions Roger Federer, Rafael Nadal and Novak Djokovic.
"It's fair to say they are three of the very best stallions to have graced our presence in many years," Jimmy George, marketing director at Tattersalls, told CNN Sport.
"The great thing about the 'Big Three' stallions is that their quality transcends all different sectors to a degree," said George. "It doesn't matter if you are looking for a two-year-old, or a classic miler, or a horse to win the Derby or the Oaks. They are producing animals in every sector ... and that's a huge part of the appeal."
Last year, Dubawi covered 174 mares, giving his owner an income of $57 million, according to thoroughbredracing.com.
The most influential stallion in recent years is the now 20-year-old Galileo, who has produced no fewer than 73 Group 1 winners and is owned by Irish billionaire John Magnier's Coolmore Stud.
His bloodline is in such demand, his stud fee is kept private. But according to thoroughbredracing.com, Galileo covered 178 mares at an estimated fee of between €400,000 ($463,000) and €600,000 ($695,196), putting his 2017 income at between €71 million ($82 million) and €107 million ($124 million).
At last week's auction for Europe's top yearlings at Tattersalls, eight horses sired by Galileo were sold for 1 million guineas or more, including a colt that fetched 3.4 million guineas on the first day of the sale.
Frankel, Galileo's unbeaten son who retired from racing having won 11 Group 1 races and close to £3 million ($4 million) prize money, covered his first mare on Valentine's Day in 2013, for a fee of £125,000 ($164,408).
Last year, he was visited by 195 mares, earning his owner, Saudi Prince Khalid bin Abdullah, $32 million.
The "Big Three" stallions earned a total of $171 million in stud fees in 2017, comfortably beating the "Big Three" of tennis --Federer, Nadal and Djokovic -- at the bank. The three tennis superstars were estimated to have made a combined $142 million last year, according to Forbes.
Although Barcelona's Messi and Ronaldo of Juventus out-earned the stallions with a combined $219 million from salaries and endorsements last year, according to Forbes, their income will drop once they quit the game.
Unlike sports stars on two legs, equine superstars can often see their currency rise once they retire and go to stud.
Take Frankel, the leading stallion at Royal Ascot this year after his offspring won three races and finished second twice.
Now 10 years of age, Frankel's owners raised his stud fee by 40% this year to £175,000 ($231,000) as his first crop of foals began to win races.
If he has his father's staying power, that means a horse that retired from racing six years ago could earn as much as $230 million in stud fees in the next decade alone.
It's the kind of money even the world's biggest soccer and tennis stars can only dream of in retirement.
No wonder high rollers such as the Qatari royal family are willing to bet big on bloodlines.
"This is the sort of horse that Sheikh Fahad and his brothers want to own," Redvers told the Tattersalls website after buying Lot 325.
A few days after the auction, Lot 325's full brother, Too Darn Hot, gave jockey Frankie Dettori his first victory in 30 years in the Dewhurst Stakes in Newmarket, cementing the two-year-old's status as the favorite for next year's 2,000 Guineas and Derby races.
For Redvers, it is now all about turning a $4.8 million gamble, the second-highest price ever paid at a European sale, into a stallion that may one day match the earning power of his famous sire, Dubawi.
"We are looking to make commercial stallions -- let's hope that he goes out and lives up to all the potential that he has," Redvers said.