The Prix de l'Arc de Triomphe is to become the second-richest horse race in the world and the most valuable on turf.
The Longchamp classic, run in early October, will be worth €4m in 2008 as a result of a new sponsorship deal with the Qatar Racing and Equestrian Association.
The race, over a mile-and-a-half, was won this year by Dylan Thomas, ridden by Kieren Fallon on what may yet turn out to be the Irishman's final ride.
It has long been regarded as racing's middle-distance championship decider.