El Gran Senor, dual Classic winner and top sire, has been put down at the age of 25.
The Northern Dancer horse won both the 2000 Guineas and Irish Derby in 1984, as well as the Dewhurst the previous year for owner Robert Sangster and trainer Vincent O'Brien.
El Gran Senor began his stud career in 1985 at his breeder EP Taylor's farm in Maryland before transferring to Ashford the following year.
'It's a sad day as El Gran Senor has been with us here since the very beginning,' Ashford manager Dermot Ryan told www.thoroughbredtimes.com.
'I'd like to make special mention of Richard Barry who has taken great care of the horse for almost 20 years.'
El Gran Senor sired a number of Group One winners including Rodrigo De Triano, Belmez, Al Hareb and Lit De Justice as well as Toussaud, who was a Grade One winner on the track before going on to be a hugely successful broodmare.