The Princess Elizabeth, since Queen of Spain, began now to manifest an uncommon wit, and to display those beauties, which proved afterwards so fatal to her.
The adverb intelligently means done in a way showing intelligence and skill. Hemp is a family of plants, some of which are used to make rope and strong cloth.
This is explained away by true believers thus: either the third brother's descendants do not know where their Cloak came from, or they know and are determined to show their ancestor's wisdom by not trumpeting the fact.