John Holles, 1st Duke of Newcastle, died in 1711. Pedigree information in the List of his widow's Duchess of Newcastle's Horses in 1712 includes:-
"Darcy's Young Sorrill, out of a Royall Mare Call'd Black Leggs & Gott by Wastell's Turk, her Dam Gott by Duke of Rutland's Black Leggs out of Darcy's oldest Royall Mare"
The Duke of Newcastle Stud papers show that the two daughters of Blacklegs Royal Mare according to the GSB (by King William's Black Barb Without a Tongue) and Oxford Dun Arabian) were probably actually out of her daughter, the Darcy Sorrill Royal Mare (which mare is not mentioned in the GSB)
The third earliest mare in the lineage of Family 7
Grandam of the great broodmare Miss Slamerkin, dam of top class racehorses Bustard (1747 King's Plate Newmarket), [Portmore's] Othello (1749 King's Plates Salisbury, Canterbury, Lewes, Newmarket, 1752 King's Plate The Curragh) and Duchess (1753 King's Plates [mares] Hambleton and Newmarket, 1754 King's Plates Nottingham, York, Lincoln and Newmarket, 1755 King's Plate Newmarket)