This morning I learned what a "levirate marriage" is. From the wiki page:
a type of marriage in which the brother of a deceased man is obliged to marry his brother's widow.Interesting. Now, who do we know who married the brother of her deceased husband? Gertrude is even referenced in the Wikipedia page as a popular culture reference.
Any connection, or purely a coincidence? I expect the latter. The technical definition of the term suggests that only *childless* widows count, and Queen Gertrude is not childless ... is she? :) While some folks like to argue that perhaps Claudius is Hamlet's real father, I don't think anybody argues that Gertrude is not his real mother.