Abd al-Muttalib
Abd al- Muttalib Shaybah ibn Hashim( c. 497 – 578) was the grandfather of Islamic prophet Muhammad.
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.
John Westley
Rev. John Westley( 1636 – 78) was an English nonconformist minister.
He was the grandfather of John Wesley( founder of Methodism).
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.
Fujiwara no Nagara
, also known as Fujiwara no Nagayoshi, was a Japanese statesman, courtier and politician of the early Heian period.
He was the grandfather of Emperor Yōzei.
Elizabeth Hay, Countess of Erroll
Elizabeth Hay, Countess of Erroll (17 January 1801 – 16 January 1856; born Elizabeth FitzClarence) was an illegitimate daughter of King William IV of the United Kingdom and Dorothea Jordan.
She married William Hay, 18th Earl of Erroll, and became Countess of Erroll on 4 December 1820 at age 19.
Due to Hay's parentage, William Hay became Lord Steward of the Household.
Elizabeth and William Hay married at St George's, Hanover Square.
Hay is pictured in a FitzClarence family portrait in House of Dun and kept a stone thrown at her father William IV and the gloves he wore on opening his first Parliament as mementos.
She died in Edinburgh, Scotland.
Agnes Duff, Countess Fife
Lady Agnes Georgiana Elizabeth Hay (12 May 1829 – 18 December 1869) was an Irish-Scottish aristocrat.
Agnes was born at Dublin, Ireland.
She was the third child of William Hay, 18th Earl of Erroll and Elizabeth FitzClarence, one of the illegitimate children of William IV and his mistress Dorothea Jordan.
Agnes died at the age of 40.
Her only son, Alexander, married Princess Louise of Wales, the eldest daughter of Albert Edward, Prince of Wales (later Edward VII) and Alexandra of Denmark (later Queen Alexandra) in 1889 and was created Duke of Fife by Queen Victoria.
Through her fourth daughter, also named Agnes, she is an ancestor of British prime minister David Cameron.
Henry Bryant (naturalist)
Henry Bryant( May 12, 1820 – February 2, 1867) was an American physician and naturalist.
He was the grandfather of Henry Bryant Bigelow.
Guillaume Wittouck
Guillaume Wittouck( 1749- 1829) was a Belgian lawyer and High Magistrate.
He was the Grandfather of industrialist Paul Wittouck.

Question: Who is the maternal grandfather of Agnes Duff, Countess Fife?
Answer: William IV of the United Kingdom