The letters, which have been discovered in Kelburn Castle in Ayrshire, show the wranglings behind the scenes as a Bill authorising the Prince of Wales to act as regent was debated in the late 18th century.
Prince George was close to the opposition party, which fully supported his claim to the regency while his father struggled with mental health problems.
The note to David Boyle, grandson of the 2nd Earl of Glasgow, from his friend James Adamson, in February 1789, states: "If the king shall continue to mend at the rate which the newspapers now give out, all the expectations and manoeuvres of what is still named the Opposition will prove in vain and pointless or at least will bear a short-lived fruit, at any rate the Regent's wings are so clipped he cannot overshadow many of his friends."
Although George III recovered before the Bill was passed, a Regency Act was passed in 1811 and the Prince of Wales acted as regent for the remainder of George III's life.
In a letter from the then Lord Boyle to his brother John on July 16, 1811, he states: "I fear the King is now in a very doubtful state."