Quickthorn is out of Daffydowndilly (Oasis Dream), a winner of three races, whose produce also includes the multiple winners Belated Breath (Bated Breath), Volturnus (Azamour), Lady Percival (Sir Percy) and the handicap winner City Streak (Cityscape). Daffydowndilly is a half-sister to Rock Eyes (Rock Of Gibraltar), who also won three races.

Second dam Art Eyes (Halling) won the Listed Noel Murless S. and was second in the Lillie Langtry S., then a Group 3. Daffydowndilly and Rock Eyes are her only winners.

Third dam Careyes (Sadler's Wells) was unraced and had eight winners, the best of them Art Eyes.

This female line is an old Aga Khan family. Fourth dam Kotama (Shahrastani) won the Listed 1000 Guineas Trial at Leopardstown.

Daffydowndilly has a yearling filly, Tardaff (Bated Breath), and a colt foal, Scarlet Legend, a full brother to Quickthorn.