Oh, shoot! I've been way of target all thse years with what I was told in my salad days : that is that there was a King of Spain who lisped and the Court mimiced his pronunciation so that the lisped pronunciation was actuallly an affectation of the Nobles which gradually oozed into the general population who aped their "betters."
An apocryphal story perhaps?
But then : in England, I was also told, the name of the river Thames was pronounced Tham-es for many years until one of the early Georges called it Tems and so it remains. The oozing into the general population following the same path : King, Nobles, comman man.
Any comment Cap?