Augustus Henry FitzRoy , 3rd Duke of Grafton , KG , PC ( 28 September 1735 â `` 14 March 1811 ) was a British Whig statesman . Augustus Henry FitzRoy , 3rd Duke of Grafton , KG , PC ( 28 September 1735 â `` 14 March 1811 ) , styled Earl of Euston between 1747 and 1757 , was a British Whig statesman of the Georgian era .