John McArthur says in his 1861 'Antiquities of Arran', that
"At Kingscross, on a hillock near the shore, there is a monolith which marks the spot from which King Robert the Bruce embarked for the Carrick coast; and in a neighbouring field, there is an unhewn block of sandstone, believed to be the sole relic of the rude cot in which the king resided, on the eve of his departure from the Island."
The RCAHMS record won't commit itself, mostly because the stone has become surrounded by a cairn of stone. The Name Book of 1864 suggests the stone stood alone at 6-7ft high, but now (or at least, in 1977) only 80cm shows out the top of a cairn. "It is possibly a Bronze Age standing stone to which a later tradition is attached, but in its present state this is conjectural."