Mary impetuously married her cousin, Lord Darnley, against the wishes of Scottish nobles. Her affection for him soon failed. He was murdered in 1567.
Mary, Queen of Scots, with her second husband, Lord Darnley
From a public domain image
Whether Mary was involved in the murder of Darnley has been a controversy ever since the murder happened. Bothwell -- Mary's next husband -- has often been blamed, and sometimes Mary herself.