I should have said Gwydir Uchaf Chapel but I can't remember seeing that stone when I was there or what it was for. It was Built by Sir Richard Wynn in 1673.
Spot on Hugo-- it is on the ground, at a strange angle, at the edge of the chapel, at the front,
No idea where it came from or why it is there, but doesn't look as though it was actually placed there.
And no BB not from there