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 the 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
A stallion advertisement in the Newcastle Courant of 23 March 1727 mentions Darcy's Oldest Royal Mare and states her sire is Darcy's White Turk
Her daughter the Blacklegs Royal Mare (by [Rutland's] Blacklegs) is her only known progeny