When Robert's son, David II, King of Scotland, became king, he spent some time in English captivity; following his release, in 1357, he restored MacDougall authority over Lorn, effectively cancelling Robert's grant to the MacRory. The 1354 quitclaim, which seems to have been an attempt to ensure peace in just such an eventuality, took automatic effect, splitting Mull from Lorn, and making it subject to the Lordship of the Isles.
When David II, son of Robert, ascended as King of Scotland, he was held captive by English forces for some time; upon his release in 1357, he reasserted MacDougall authority over Lorn. This action nullified Robert's grant to the MacRory. The 1354 quitclaim, intended to ensure peace in similar circumstances, automatically took effect, dividing Mull from Lorn and subjecting it to the Lordship of the Isles.