Do you know why the spanish letter "j" is pronounced as "h"?

Do you know why the spanish letter "j" is pronounced as "h"?

because Francisco Franco made a typo and didn't want to admit his mistake. He forced the people to change the pronunciation instead of admitting he was fallible.

[ Hahah..an original joke you guys, can you believe it? I had to google Spanish dictator and Francisco Franco was the name that came up]