LONDON—One of Queen Elizabeth II’s racehorses has failed a doping test.

Six-year-old Moonlit Path tested positive for a banned substance that prevents hemorrhaging after a sixth-place finish in her debut February at Huntingdon.

Trainer Nicky Henderson has been charged with breaching two rules by the British Horseracing Authority.

The queen’s racing manager, Michael Oswald, described it as “very disappointing news” and told British media that the monarch had been informed.

Henderson acknowledged the use of the substance, but said it was not used as doping.

Moonlit Path has run twice since her debut, finishing fourth out of 13 on both occasions.