prime minister was apparently Lord Grey who in wedlock fathered ten sons and six daughters in addition to one illegitimate daughter by Georgiana Cavendish, Duchess of Devonshire who was subsequently raised by Grey's parents. Kindred PMs At least 24 British prime ministers were related to at least one other prime minister by blood or marriage. Fathers and sons Two sets of father and son have successively held the office: Lord Chatham (aka "Pitt the Elder") and William Pitt the Younger George Grenville and William, Lord Grenville Brothers The only brothers to hold the office were Henry Pelham (PM 1743–54) and his older brother and immediate successor Thomas Pelham-Holles, 1st Duke of Newcastle (PM 1754–56, 1757–62). Full cousins Pitt the Younger and Lord Grenville (who directly succeeded the former in office) were the only set of full cousins to hold the office, their fathers being brothers-in-law. Uncles and nephews There have been two blood uncle-nephew sets of prime ministers. George Grenville and William Pitt the Younger Robert Gascoyne-Cecil, 3rd Marquess of Salisbury and Arthur Balfour, who succeeded Salisbury in office after the former's last term. The phrase "Bob's your uncle" is said to have originated in connection with this set, from ministerial promotions Balfour gained under Salisbury. Great-great-uncle and great-great-nephew Lord Wilmington was two-greats uncle of Spencer Perceval, whose mother, Catherine (née Compton), Baroness Arden, was a blood great-niece of Wilmington. Father-in-law and son-in-law The Duke of Portland, married in 1766 Lady Dorothy Cavendish, daughter of the Duke of Devonshire (who had died in 1764). Brothers-in-law Pitt the Elder was married from 1754 to George Grenville's sister Hester. Lord Palmerston was married from 1839 to Lord Melbourne's sister Emily, dowager Countess Cowper. Uncles-in-law and nephews-in-law William Pitt the Elder married Hester Grenville who was the sister of George Grenville and the aunt of William Grenville, which makes William Pitt the Elder the uncle-in-law of William Grenville. Winston Churchill and Anthony Eden. In 1952, during Churchill's second term, Eden married Clarissa, daughter of John Strange Spencer-Churchill, Winston's brother, before succeeding to the office. Great-uncle-in-law and great-nephew-in-law Lord Grenville was married from 1792 to Anne Pitt, daughter of Thomas Pitt, 1st Baron Camelford who was a nephew of William Pitt the Elder. Great-great-great-grandfather and great-great-great-grandson Alec Douglas-Home was the great-great-great-grandson of Lord Grey. Great-great-great-uncle and great-great-great-nephew Lord Russell and Alec Douglas-Home. Education The first prime minister never to have been a university graduate