Okay; the oft-cited fact that "Henry IV was the first English monarch after 1066 whose first language was English".
Now, while I have no doubt it was, what I find puzzling about this is that his predecessor was his cousin, Richard II (their fathers were brothers).
We know that their grandfather, Edward III, spoke English (he seemed to prefer English language tournament mottoes to French ones), even if Norman French was his first language, and we sources that document patrilineal ancestors of them both that have an understanding of English varying between a rough working knowledge (Henry II, Edward II) to outright fluency (Edward I, who learned it as a child), even if it wasn't their first language.
So what I'm finding most confusing about is, why would Richard II have been raised speaking (Norman-)French, and Henry IV English, when both men were raised at the same time, in related households, in the same family, in the same country (Richard II was born in Bordeaux but seems to have been raised in England), both to mothers who were English-born?
What is the source regarding Henry IV being the first to speak English as their first language, and Richard the last? I can't for the life of me find any sources in respect to either.