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.
William Hay, 10th Earl of Erroll
William Hay, 10th Earl of Erroll PC (before 1597 – 7 December 1636) was a Scottish nobleman.
William Hay, 1st Earl of Erroll
William Hay, 1st Earl of Erroll (1423 – October 1462) was a Scottish peer.
His was the first Earl of Erroll and the second Lord Hay of Erroll.
Nicholas Hay, 2nd Earl of Erroll
Nicholas Hay, 2nd Earl of Erroll( – 1470) was a Scottish peer.
He was the second Earl of Erroll and the third Lord Hay of Erroll.
William Hay, 6th Earl of Erroll
William Hay, 6th Earl of Erroll( 1521 – 11 April 1541), styled as Lord Hay until age 1, was a Scottish peer.
James Hay, 15th Earl of Erroll
James Hay, 15th Earl of Erroll (20 April 1726 – 3 July 1778) was a Scottish nobleman and the son of William Boyd, 4th Earl of Kilmarnock.
William Hay, 3rd Earl of Erroll
William Hay, 3rd Earl of Erroll (– 14 January 1507) was a Scottish peer.
He was the third Earl of Erroll and the fourth Lord Hay of Erroll.
William Hay, 5th Earl of Erroll
William Hay, 5th Earl of Erroll( – 28 July 1522) was a Scottish peer and statesman.
James Erskine Wemyss
James Erskine Wemyss( 9 July 1789 – 3 April 1854) was a Scottish MP and Rear- Admiral.
He was the son of William Wemyss by his wife Frances, daughter of Sir William Erskine, 1st Baronet.
In 1820 he succeeded his father as Member of Parliament for Fife, sitting until 1831.
He represented the county again from 1832 to 1847.
By his wife Lady Emma, daughter of William Hay, 17th Earl of Erroll, he was father of James Hay Erskine Wemyss, also later MP for Fife.
William Hay, 17th Earl of Erroll
William Hay, 17th Earl of Erroll (12 March 1772 – 26 January 1819), known as Lord Hay until 1778, was a Scottish peer.
In 1805, he was appointed Knight Marischal.
Erroll was the son of James Hay, 15th Earl of Erroll and his second wife, Isabella Carr.
He firstly married Jane Bell (d. 1793) in 1792, and they had one child together.
Secondly, he married Alicia Eliot (d. 1812) in 1796, who was the sister-in-law of Sir Thomas Stapleton, 6th Bt.
(also 16th Baron Le Despencer); they had seven children.
Finally, Erroll married Harriet Somerville (d. 1864) in 1816.

Question: Who is the paternal grandfather of William Hay, 17Th Earl Of Erroll?
Answer: William Boyd, 4th Earl of Kilmarnock