King Robert the Bruce had requested that Douglas, latterly his most esteemed companion in arms, should carry his heart to the Holy Land, as atonement for the murder of John III Comyn. Douglas and his knights had been invited to join the forces of Alfonso XI of Castile, Edward III of England's cousin by his mother Queen Isabella, to fight against the Moors in 1330 at the siege of Teba. Outnumbered and cut off from the main Christian force, Douglas was killed leading a cavalry charge. The casket containing the heart of the Bruce was recovered and returned to Scotland, to be interred at Melrose Abbey. Douglas' bones were boiled and returned to Scotland; his embalmed heart was recently recovered in the Douglas vaults at the Kirk of St Bride but his bones are not in the stone vault lying under his effigy and they have yet to be located.