I have that episode on tape from last year.
Yes, it was Royal Stewart as I recall, and Cawdor was the only Scottish castle he visited. The others were south of the border & I'd have to go back and watch it to recall which they were.

One bit I would mention, when he wore the kilt was I noticed he wore a belt even though he wore a vest under his coat. It just didn't look right & kept bugging me! Oh well...