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 "her Dam Gott by Duke of Rutland's Black Leggs" is this Blacklegs Royal Mare which is the traditional foundation mare of Family 7, so this pedigree information extends the family back a further generation and shows that Darcy's Oldest Royal Mare is the Foundation Mare of Family 7
The second earliest mare in the lineage of Family 7
The GSB says she has two daughters, by King William's Barb Without a Tongue and by the Oxford Dun Arabian; however the Duke of Newcastle Stud papers show that the Blacklegs Royal Mare's daughter was the Darcy Sorrill Royal Mare (1703, by Wastell's Turk), and that the two mares above, credited in the GSB as her daughters are probably actually her granddaughters out of the Darcy Sorrill Royal Mare