General Sir Brent Spencer's military career is sketched briefly at Wikipedia. In 1800 he met Princess Augusta Sophia, one of the many daughters of George III. They had a long relationship. His will was proved 16 April 1829 and is at Kew (PROB 11/1754/426). The Canning family for many years had a miniature of the princess, which was bought by the royal family.
"Now  Princess Augusta dreamt of having Sir Brent Spencer not only for a lover but for a husband, as she later recounted. But she did not yet reveal her feelings, strong though they were, to Spencer himself. He, for his part, caused much ill feeling when he unaccountably broke his engagement to his cousin Miss Canning this year, but whether this was on account of unspokane feelings he had himself for Princess Augusta cannot be known." [Princesses, by Flora Fraser]
In 1815, Sir Brent Spencer replaced his brother, Joshua Spencer, as MP for Sligo, pursuant to arrangements made with their nephew, George Canning (1st Baron Garvagh).
The given name of General Sir Brent Spencer's mother apparently was Mary.
Sir Brent Spencer apparently had a son by Mrs. Harriet Eleanor Pelham.
"QUEEN SQUARE. THE PELHAM CASE. "Lord Garvagh had been an intimate friend of Sir B. Spencer, and had promised to do for his son that which had been done for the late Mr. [George] Canning; but the young man's habits and turn of mind prevented that advancement, for, although he was most gentlemanly in his manners, and so specious in his discourse that one would fain believe him, he was carried away by every passing folly or vice, and was so strange in his behavior that he had been actually expelled the University of Cambridge for lying in bed fourteen successive days and nights ." [newspaper cutting, unidentified, from family scrapbook]
Akihito Suzuki, in her 2006 book MADNESS AT HOME, at p. 166, states that General Spencer's illegitimate son by Mrs. Pelham was 34 years old on 18 May 1844 when the magistrate sent police to Mrs. Pelham's house in Chelsea.
In 1795, Lt.-Col. Brent Spencer was engaged to Frances Canning, sister of Paul Canning (brother-in-law of Brent Spencer). George Canning, the future Prime Minister, "regarded Spencer as a blackguard as a result of the financial terms he insisted on as part of the match, and his own claim to 4,000 [pounds] prize money for his efforts in the West Indies campaign. Canning MSS. (13), C[anning] to Rev. William Leigh, 8, 22 June 1795."
Sir Brent Spencer was "a great favourite of George III, [who] made him one of his equerries, and spent much time at court."
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