Question: The husband of Kathleen Kennedy was heir apparent to the 10th Duke of where?

Context paragraphs:
Yukou: Crown Prince Yukou (; died 672 BC) was the original heir apparent of Duke Xuan of Chen, the sixteenth ruler of the ancient Chinese state of Chen during the Spring and Autumn period.  In 672 BC, the 21st year of his reign, Duke Xuan's favourite concubine gave birth to a son named Kuan.  Duke Xuan killed Yukou and made Kuan his new heir apparent.

Charles, Prince of Wales: Charles, Prince of Wales (Charles Philip Arthur George; born 14 November 1948) is the eldest child and heir apparent of Queen Elizabeth II.  Known alternatively in Cornwall as Duke of Cornwall and in Scotland as Duke of Rothesay, he is the longest-serving heir apparent in British history, having held the position since 1952.  He is also the oldest person to be next in line to the throne since Sophia of Hanover (the heir presumptive to Queen Anne), who died in 1714 at the age of 83.

Walter Scott, Earl of Dalkeith: Walter John Francis Montagu Douglas Scott, Earl of Dalkeith (born 2 August 1984) is a British nobleman.  He is the second child and elder son of Richard Montagu Douglas Scott, 10th Duke of Buccleuch & 12th Duke of Queensberry, and Lady Elizabeth Kerr, a daughter of Peter Kerr, 12th Marquess of Lothian and Antonella Reuss Newland.  He is heir apparent to the Dukedoms of Buccleuch and Queensberry.

William Cavendish, Marquess of Hartington: Major William John Robert "Billy" Cavendish, Marquess of Hartington (10 December 1917 – 9 September 1944) was an English politician and soldier.  He was the elder son of Edward Cavendish, 10th Duke of Devonshire, and his wife, Lady Mary Gascoyne-Cecil.  He was the husband of Kathleen Kennedy, sister of the future U.S. President John F. Kennedy.

Charles Gordon-Lennox, 10th Duke of Richmond: Charles Henry Gordon-Lennox, 10th Duke of Richmond, 10th Duke of Lennox, 10th Duke of Aubigny, 5th Duke of Gordon (19 September 1929 – 1 September 2017), styled Lord Settrington until 1935 and Earl of March and Kinrara between 1935 and 1989, was an English peer and landowner.

Kathleen Cavendish, Marchioness of Hartington: Kathleen Agnes Cavendish, Marchioness of Hartington ("née" Kennedy; February 20, 1920 – May 13, 1948), also known as "Kick" Kennedy, was an American socialite.  She was the daughter of Joseph P. Kennedy, Sr. and Rose Kennedy, sister of future U.S. President John F. Kennedy, and wife of the Marquess of Hartington, heir apparent to the 10th Duke of Devonshire.

Prince of Beira: Prince of Beira (Portuguese: "Príncipe da Beira" ) is a title traditionally granted to the heir apparent of the heir apparent to the throne of Portugal.  The title's original use that it be granted on the eldest daughter of the reigning monarch of Portugal.  Tied with the title of Prince of Beira, is Duke of Barcelos, as heir to the Duke of Braganza and Prince of Brazil ("later" Prince Royal of Portugal).  The current Prince of Beira is Prince Afonso, the eldest son of Duarte Pio, Duke of Braganza.

Charles Howard, 10th Duke of Norfolk: Charles Howard, 10th Duke of Norfolk, Earl Marshal (1 December 1720 – 31 August 1786), was an English peer and politician.  He was the son of Henry Charles Howard (c. 1668–1720) and Mary Aylward (c. 1670–1747).  He married Catherine Brockholes (before 1724–1784), daughter of John Brockholes, on 8 November 1739.  He succeeded to the title of Duke of Norfolk in 1777 after the death of Edward Howard, 9th Duke of Norfolk.  Charles Howard, 10th Duke of Norfolk died on 31 August 1786 at age 65.  He was succeeded by his son, Charles Howard, 11th Duke of Norfolk.

Baron of Renfrew (title): Baron of Renfrew is a dignity held by the heir apparent to the British throne, currently Prince Charles.  It was held by the Scottish heir apparent beginning in 1404.  It is closely associated with the title Duke of Rothesay.  An act of the Scottish Parliament passed in 1469 confirmed the pattern of succession.  Renfrew, a town near Glasgow, is sometimes called the "cradle of the royal Stewarts."

Duke of Rothesay: Duke of Rothesay (Scottish Gaelic: "Diùc Baile Bhòid" , Scots: "Duik o Rothesay" ) is a dynastic title of the heir apparent to the British throne, currently Prince Charles.  It was a title of the heir apparent to the throne of the Kingdom of Scotland before 1707, of the Kingdom of Great Britain from 1707 to 1801, and now of the United Kingdom of Great Britain and Northern Ireland.  It is the title mandated for use by the heir apparent when in Scotland, in preference to the titles "Duke of Cornwall" (which also belongs to the eldest living son of the monarch, when and only when he is also heir apparent, by right) and "Prince of Wales" (traditionally granted to the heir apparent), which are used in the rest of the United Kingdom and overseas.  The Duke of Rothesay also holds other Scottish titles, including those of Earl of Carrick, Baron of Renfrew, Lord of the Isles and Prince and Great Steward of Scotland.  The title is named after Rothesay on the Isle of Bute, Argyll and Bute, but is not associated with any legal entity or landed property, unlike the Duchy of Cornwall.

Supporting paragraphs: William Cavendish, Marquess of Hartington Kathleen Cavendish, Marchioness of Hartington
Answer: Devonshire