Sir Thomas Sempill fell fighting in support of King James III of Scotland at the Battle of Sauchieburn in June 1488. His only son, John Sempill, inherited the family estates. John was made Lord Sempill during the reign of King James IV of Scotland. In 1505 John founded the Collegiate church of Lochwinnoch. He also rebuilt the castle at the eastern end of the loch which he renamed Castle Sempill. He was killed fighting for the king at the Battle of Flodden in 1513. (See: John Sempill, 1st Lord Sempill).