Roaring Lion beat stablemate Enable to be named Horse of the Year as trainer John Gosden had a record-equalling night at the Cartier Racing Awards.
The winner of four top-level Group One races, Roaring Lion also secured the top three-year-old colt honour.
Enable, who won the Breeders' Cup Turf and a second Prix de l'Arc de Triomphe, took the older horse award.
Top stayer Stradivarius and two-year-old colt Too Darn Hot completed the list of five awards for Gosden horses.
Roaring Lion, owned by Qatar Racing, won three Group One mile-and-a-quarter races from July to September - the Coral-Eclipse at Sandown, York's Juddmonte International and the Qipco Irish Champion Stakes at Leopardstown.
The son of Kitten's Joy followed up with victory in the one-mile Queen Elizabeth II Stakes at Ascot before finishing last on his final run in the Breeders' Cup Classic.
It is the fourth time in five years Gosden has trained the horse of the year in European Flat racing's end of season awards - after Kingman (2014), Golden Horn (2015) and Enable (2017).
Stradivarius, also trained by Gosden, and Jessica Harrington's filly Alpha Centauri were the other nominations - along with Enable - for the main award.
All the awards
(Horse, trainer, owner)
Horse of the year: Roaring Lion (John Gosden/Qatar Racing)
Older horse: Enable (John Gosden/Khalid Abdullah)
Stayer: Stradivarius (John Gosden/Bjorn Nielsen)
Sprinter: Mabs Cross (Michael Dods/ David & Emma Armstrong)
Three-year-old colt: Roaring Lion (John Gosden/Qatar Racing)
Three-Year-old filly: Alpha Centauri (Jessica Harrington/Niarchos family)
Two-year-old colt: Too Darn Hot (John Gosden/Lord Lloyd-Webber)
Two-year-old filly: Skitter Scatter (Patrick Prendergast for Anthony Rogers and his mother Sonia.
Award of Merit: David Oldrey, administrator, owner-breeder and racing historian, he worked with the Jockey Club, the British Horseracing Board and numerous other bodies in the racing industry.