Alexander Seton, 5th of Mounie (of the second family), was born in 1815, son of Alexander Seton, 4th of Mounie and Janet Ogilvy of Airlie.  At the time of his succession to his father he was a Major in the 74th Highlanders Regiment.

He became Lieutenant-Colonel of the Regiment in 1851, and was known for his gallant actions during the sinking of the HMS Birkenhead in 1852. 

1096 Sergeant David Andrews " S ", later Staff Sgt Major of the 60th KRRC (now the Royal Greenjackets), wrote a letter to Mr. David Seton, brother of Colonel Alexander Seton, the senior Army Officer on board the vessel, describing the gallantry displayed by Colonel Seton.

"Lt Colonel Alexander Seton of Mounie, Aberdeenshire.  Senior Army Officer aboard ship. Was on his way to command the 74th of Foot in The 8th Frontier War 1846-1858. A fine Officer who controlled the men aboard the ship so that the women and the children would get away first, he also delayed the men from swimming for their lives, until the life boats had rowed well away from the side of the ship.   Lieutenant-Colonel Seton, whose high-mindedness, self-possession, and calm determination inspired all on board, was son and heir of the late Alexander Seton, Esq. of Mounie, Aberdeenshire, and represented the Mounie branch of the old and eminent Scottish house of Pitmedden. His death was undoubtedly a great loss to the British army, as all who knew him agree in stating that he was a man of high ability and varied attainments; he was distinguished both as a mathematician and a linguist. Lord Aberdare (formerly the Right Honourable H. A. Bruce) speaks of Colonel Seton, from personal knowledge, as "one of the most gifted and accomplished men in the British army."