Mather Byles Brown was an American artist, born in Boston, who came to London at an early age and probably became a pupil of Benjamin West. Although he was described in 1789 as Portrait-Painter to the Duke of York, this and 404042 are the only two paintings by him in Royal Collection. Mather Brown had a long career, exhibiting at the Royal Academy for nearly fifty years between 1782 and his death in 1831. 

This portrait shows the Prince of Wales wearing an imaginary military uniform, probably designed by the Prince himself. The buttons are those of a General Officer, although the Prince was not at this date in the army. The buckle on the sword-belt is embellished with the Prince of Wales's arms and feathers. Draped on the table behind is a voluminous red state robe lined with ermine, while to the left is the blue velvet mantle of the Order of the Garter. The collar of the Order of the Garter is depicted alongside a crown. In the background is a fort with guns firing and warships at sea. 

A receipt presented by the artist to the Prince in 1791 records the payment of 140 guineas 'To a very large extra-sized Whole Length of His Highness, painted two years ago, and present to The Rt Hon. Ld Lougborough'. It is tempting to suggest that this is the painting to which is refers, and would therefore show the Prince at the age of 27. The painting does not seem to have been owned by the Prince himself, being first recorded in the royal Collection in 1876. 

There are considerable pentimenti. The column was added to the design - originally the sky continued behind the figure of the Prince and the curtain is visible behind the column with the naked eye. There are also amendments to the shape of the coat, the position of the Garter badge and the direction of the left arm. The papers under the left arm were also altered. At first they had traces of writing on them, apparently addressed to the Prince, and there are traces on the scroll of a similar address. The crown on the table alongside was originally placed higher.