The situation changed again on 10 February 1306 , when Robert the Bruce murdered his rival John Comyn and a few weeks later , on 25 March , had himself crowned king of Scotland by Isobel , sister of the Earl of Buchan .
The situation changed again , in 1306 , when de Brus murdered his rival John Comyn and had himself crowned King of Scotland by Isobel , sister of the Earl of Buchan .