Question: Who is the paternal grandfather of Robert Petre, 9Th Baron Petre?

Knowledge 1: Robert Petre, 9th Baron Petre
Robert Edward Petre, 9th Baron Petre (March 1742 in Ingatestone Hall – 2 July 1801) was a British peer.Lord Petre was the son of Robert Petre, 8th Baron Petre (1713–1742), a renowned horticulturist, and Lady Henrietta Anna Mary Barbara Radclyffe (1714–1760), daughter of the 3rd Earl of Derwentwater (1689–1716) who was the grandson of Charles II by his mistress Moll Davis.Lord Petre was a member of the English Roman Catholic nobility, a philanthropist and responsible for employing James Paine to design a new Thorndon Hall and a house in Mayfair. [SEP] Knowledge 2: Robert Petre, 8th Baron Petre
Robert James Petre, 8th Baron Petre (3 June 1713 – 2 July 1742) was a renowned horticulturist and a British peer.Lord Petre was the son of Robert Petre, 7th Baron Petre (1689–1713) and his wife Catherine Walmesley (1697 – 31 January 1785), heiress of the Walmesley family of Lancashire.Petre was born three months after his father's death and spent his childhood at Ingatestone Hall, instead of at Thorndon Hall, the family seat, as his grandmother was still in residence there.
Knowledge 1: Robert Petre, 9th Baron Petre
Robert Edward Petre, 9th Baron Petre (March 1742 in Ingatestone Hall – 2 July 1801) was a British peer.Lord Petre was the son of Robert Petre, 8th Baron Petre (1713–1742), a renowned horticulturist, and Lady Henrietta Anna Mary Barbara Radclyffe (1714–1760), daughter of the 3rd Earl of Derwentwater (1689–1716) who was the grandson of Charles II by his mistress Moll Davis.Lord Petre was a member of the English Roman Catholic nobility, a philanthropist and responsible for employing James Paine to design a new Thorndon Hall and a house in Mayfair. [SEP] Knowledge 2: Charles Stourton, 15th Baron Stourton
Charles Stourton, 15th Baron Stourton (2 March 1702 – 11 March 1753) was the son of Charles Stourton (1669–1739), himself the third son of William Stourton, 12th Baron Stourton.Charles' mother was Katherine Frompton (died 1736).Charles was the eldest of five children, with one brother and sisters; Mary (1706–1764), Jane (1708–1769) and Katherine (1710–1777).Charles succeeded his childless uncle Thomas in 1744 and was succeeded by his brother William in 1753.He married Catherine Walmesley (1697 – 31 January 1785), widow of Robert Petre, 7th Baron Petre, on 2 April 1733.They had no children.
Knowledge 1: Robert Petre, 9th Baron Petre
Robert Edward Petre, 9th Baron Petre (March 1742 in Ingatestone Hall – 2 July 1801) was a British peer.Lord Petre was the son of Robert Petre, 8th Baron Petre (1713–1742), a renowned horticulturist, and Lady Henrietta Anna Mary Barbara Radclyffe (1714–1760), daughter of the 3rd Earl of Derwentwater (1689–1716) who was the grandson of Charles II by his mistress Moll Davis.Lord Petre was a member of the English Roman Catholic nobility, a philanthropist and responsible for employing James Paine to design a new Thorndon Hall and a house in Mayfair. [SEP] Knowledge 2: Robert Petre, 7th Baron Petre
Robert Petre, 7th Baron Petre( 1689 – 22 March 1713) was a British peer, the son of Thomas Petre, 6th Baron Petre( 1633 – 1706) and his wife Mary Clifton, daughter of Sir Thomas Clifton.He succeeded to his title, at the age of 17, upon the death of his father.Robert is said to have spurned wearing a wig in the conventional way, spending instead six hours every day dressing his own hair.He caused an uproar of indignation and outrage in the family when, in 1711, being then only 21, in a freak of gallantry cut off a lock of hair from the head of a celebrated beauty, his distant cousin, Arabella Fermor, daughter of Henry Fermor of Tusmore, Oxfordshire.

Answer: Robert Petre, 7th Baron Petre