Robert E. Preston
Robert E. Preston( 1836–1911) was Director of the United States Mint from 1893 to 1898.
Robert Preston Bruce
Hon.
Robert Preston Bruce DL (4 December 1851 – 8 December 1893) was a British Liberal Party politician.
Bruce was the second son of James Bruce, 8th Earl of Elgin and his second wife, Lady Mary Louisa Lambton, daughter of the 1st Earl of Durham.
He was educated at Eton College and Balliol College, Oxford.
He was a captain in the Fifeshire Artillery Militia from 1877 to 1881 and was a J.P. and Deputy Lieutenant for Fifeshire.
Bruce was elected at the 1880 general election as the Member of Parliament (MP) for Fife.
When the seat was divided under the Redistribution of Seats Act 1885 he stood and was elected unopposed for the new Western division of Fife.
He was re-elected unopposed in 1886, and resigned his seat on 21 June 1889 by becoming Steward of the Manor of Northstead.
Preston Austin
Preston Bruce Austin( 9 December 1827 – 7 July 1908) was a Welsh clergyman, barrister and cricketer.
Mary Louisa Bruce, Countess of Elgin
Mary Louisa Bruce, Countess of Elgin and Kincardine (8 May 1819 – 9 March 1898) was the daughter of John Lambton, 1st Earl of Durham and his second wife Louisa Elizabeth Lambton
(née Grey), daughter of Charles Grey, 2nd Earl Grey.
She travelled to Canada twice: the first time when her father went to Canada to investigate the Lower Canada Rebellion in 29 May – 1 November 1838.
She later returned to Canada with her husband, James Bruce, 8th Earl of Elgin, from 1847 to 1853.
An accomplished artist, she studied under John Richard Coke-Smyth, alongside her sister, Lady Emily Augusta, and travel companion, Katherine Ellice.
She wrote and illustrated journals and diaries of her international travels.
Prithvipati Shah
Prithvipati Shah( ?–1716) was the king of the Gorkha Kingdom in the Indian subcontinent, present- day Nepal.
He was the grandfather of Nara Bhupal Shah.
Lyon Cohen
Lyon Cohen( 1868–1937) was a Polish- born Canadian businessman and a philanthropist.
He was the grandfather of singer/ poet Leonard Cohen.
Kaya Alp
Kaya Alp was, according to Ottoman tradition, the son of Kızıl Buğa and the father of Suleyman Shah, who was, in turn, the grandfather of Ertuğrul, and the great grandfather of the Ottoman Empire founder, Osman I.
Guillaume Wittouck
Guillaume Wittouck( 1749- 1829) was a Belgian lawyer and High Magistrate.
He was the Grandfather of industrialist Paul Wittouck.
John Westley
Rev. John Westley( 1636 – 78) was an English nonconformist minister.
He was the grandfather of John Wesley( founder of Methodism).
Abd al-Muttalib
Abd al- Muttalib Shaybah ibn Hashim( c. 497 – 578) was the grandfather of Islamic prophet Muhammad.

Question: Who is Robert Preston Bruce's maternal grandfather?