https://www.britannica.com/story/is-castilian-spanish-spoken-with-a-lisp
The myth of the Spanish king’s lisp has been attributed to at least two monarchs: Ferdinand III, king of Castile from 1217 to 1252 and of Leon from 1230 to 1252, and Peter the Cruel, king of Castile and Leon from 1350 to 1369. In court historian Pedro López de Ayala’s Crónicas, the latter is said to have “spoken with a slight lisp,” an observation often taken out of context to support the theory of a Castilian speech impediment. But Ayala never claimed that others in court mimicked Peter’s way of speaking, nor was the lisp at all the subject of his writing.
Ayala is one of Peter the Cruel’s only contemporaries to mention the king’s lisp; no historical evidence exists that suggests that it—or Ferdinand III’s alleged lisp, of which no record survives—influenced other Spanish speakers. Claims that Castilian Spanish is spoken with a lisp are based on rumor, not fact.
Edit: > For anyone who hasn’t learned the history, that speaking impediment is literally how the pronunciation came about
Oy vey.
I’m sorry, I’m not going to go back and forth with this person. I know I’m coming off like a “well, actually” dick here but that’s not a pedantic minor difference. It was objectively false.
Scholars are still debating. One can only hope.