I just finished watching the "Madness of King George" and I can't imagine it was actually used.
hi. While you may get answers here, it may be worth x-posting to one of the language-related subs like /r/AskLinguistics or /r/Etymology
Christopher Hibbert in his George III: A Personal History (London: Basic, 2000), pp. 184-185 says:
Miss Burney was to become well accustomed to the King's unnerving manner of conducting a conversation, his habit of walking restlessly about the room to ask a question of one person followed by a 'What? what? what?' in a tone of voice at once good-natured and hectoring, then turning away to repeat the answer to someone else.
Lady Louisa Stuart, daughter of George III's favourite Lord Bute, wrote in her memoir "a mighty scope for satire was afforded...by the King's trick of saying What? What?" (Lady Louisa Stuart, Some Account of John Duke of Argyll and His Family (London: W. Clowes & Sons, 1864), p. 110).
A Gillray cartoon from 1791 depicted George's enemy Charles James Fox executing George, with George exclaiming ‘What! What! What! What's the matter now?’