of the ordnance. Since his reconciliation with the court Marlborough had deserted Carteret for Fox, and at the latter's secret marriage with Lady Caroline Lennox had given away the bride. In 1754 Marlborough advised his new leader to moderate his demands and to give a pledge not to oppose Pitt, and in October 1756 wrote to Bedford suggesting a junction between the rivals (Bedford Corresp. ii. 204). In the following year Marlborough, together with Lord George Sackville and General Waldegrave (afterwards third earl), conducted an inquiry into the failure of the expedition against Rochefort, ‘with the fairness of which people are satisfied’ (Mann to Walpole, 20 Nov. 1757).
In May 1758 Marlborough was given the command of an expedition directed against St. Malo, but was himself ‘in reality commanded by Lord G. Sackville’ (Walpole to Mann, 10 Feb. 1758). The expedition consisted of eighteen ships of the line, thirteen frigates, and three sloops, with four fireships and two bomb-ketches, carrying fourteen thousand soldiers and six thousand marines. As volunteers Marlborough is said to have taken with him ‘half of the purplest blood of England’ (ib. 11 June). Sailing on 1 June, the troops landed without opposition in Cancale Bay, but found the town of St. Malo too strongly fortified to be attacked. After setting on fire some naval stores, three warships, and some privateers and merchantmen, the men were immediately re-embarked. The expedition next appeared before Granville and Cherbourg, but was prevented by the weather from attacking either, and had to return owing to sickness and want of water. On 1 July the squadron anchored at Spithead, where it remained for orders till the 6th, while ministers disputed whether or not the troops should be landed (Dodington, Diary). Fox applied to the undertaking the fable of the mountain and the mouse, and the king ‘never had any opinion of it;’ but Prince Ferdinand acknowledges that as a diversion it had materially assisted him in his campaign in western Germany by preventing the French from sending reinforcements. No discredit attached to Marlborough, though, as Walpole says, he lacked experience and information. He was now despatched to Germany in command of an English contingent which was to join Prince Ferdinand. He landed at Embden with ten thousand men on 10 July, and successfully effected his junction with the German troops in Westphalia. Before being able to take part in any important operations he died suddenly at Munster on 20 Oct. 1758. The cause of death was announced to be dysentery, but some thought he had been poisoned, as he had recently received letters threatening him with death by that means. The supposed author of these, however, having been apprehended by the order of Sir John Fielding, had been acquitted (Ann. Reg. 1758, pp. 121–6), and there seems to be no ground, other than a chance coincidence, for suspecting foul play (cf. Notes and Queries, 6th ser. iii. 453, iv. 16, 17). Marlborough's talents were pre-eminent neither in war nor in politics, but were respectable in both. Aaron Hill [q. v.] in a poem, ‘The Fanciad,’ published anonymously in 1743, addressed him ‘on the turn of his genius to arms’ in a tone of light ridicule. As a governor of the Charterhouse and the Foundling Hospital he assisted education and philanthropy.
The descriptions of his character given by Walpole and Hervey agree in their main points, though the former dwells on his good sense, modesty, and generosity, while the latter prefers to touch on his want of information, carelessness, and profuseness. Walpole says that his brother, John Spencer, left the Sunderland property in reversion to Pitt, ‘notwithstanding more obligations and more pretended friendship for his brother the duke than is conceivable.’ Besides the ill-will of his grandmother, Marlborough had for long to contend with the strong dislike felt for him by George II, which was largely due to his being the son of Lord Sunderland. The king, says Hervey, never spoke of him without some opprobrious epithet. His ill-will may have been increased by a scheme of the old duchess, discovered and frustrated by Walpole, to marry Marlborough's sister, Lady Diana Spencer, to Frederick, prince of Wales.
Two portraits of the third Duke of Marlborough by Van Loo are at Blenheim, as well as one by Hudson representing the duchess and her family.
By his marriage in 1732 with Elizabeth Trevor, daughter of Thomas, second lord Trevor of Bromham, Marlborough had three sons and two daughters. Of the daughters, Lady Diana Spencer married the second Viscount Bolingbroke, and Lady Elizabeth the tenth Earl of Pembroke. The latter, generally known as Lady Betty, is described by Walpole as ‘divinely beautiful in the Madonna style.’ In 1762 her husband, disguised as a sailor, ran off with a beauty named Miss Hunter, leaving a letter testifying to his wife's virtue (Walpole, Letters, iii. 490–2). Lady Betty survived till 30 April 1831, when she was ninety-three. The eldest son, George, fourth duke of Marlborough [q. v.], is separately noticed.