John Wilkes’ Wikipedia article is here. Mary Wilkes' article in the peerage is here; she never married.
He is a distant relative of the most infamous assassin in the USA’s assassination-plagued history, John Wilkes Booth.
From the-athenaeum.org.
Mary wears a polonaise and sheer apron in this Zoffany portrait.
Keywords: Zoffany, Mary Wilkes, Polly Wilkes, Wilkes family, British, high large curl coiffure, feathered floral headdress, earrings, fitted bodice, U-décolletage, neckline ruff, three quarter length close sleeves, ruched arm bands, bows, cuffs, vee waistline, pouff over-skirt, ruched ruffle, apron, maxi-length full skirt, flounces, gloves