"most like the picture of Lady Ranelagh, and I have heard more still to the famous Duchess of Mazarine"
Portrait of Hortense Mancini, duchesse de Mazarin, 1675
Public DomainPortrait of Hortense Mancini, duchesse de Mazarin, 1675 - Credit: Jacob Ferdinand Voet

Katherine Jones, Viscountess Ranelagh (1615 - 1691) was a leading Anglo-Irish intellectual.  She was the daughter of Richard Boyle, 1st Earl of Cork. She married Arthur Jones, 2nd Viscount Ranelagh, in 1630.  She left Ireland after the rebellion of 1641, and moved to London. 

Hortense Mancini, duchesse Mazarin (1646 – 1699) was the favourite niece of Cardinal Mazarin, chief minister of France, and a mistress of Charles II, King of England.  Charles in fact proposed, but as he was in exile at the time, Cardinal Mazarin rejected the offer, thinking he had limited prospects (Charles was reinstated as King of England a few months later).  Hortense was the fourth of five famous Mancini sisters, who along with two of their female Martinozzi cousins, were known at the court of King Louis XIV of France as the Mazarinettes, and renowned for their beauty.