My iPhone thinks Android is an IPhone

I am on iPhone 8plus. I have been texting my android user for years on my iPhone. BUT ONE PARTICULAR FRIEND OF MINE, My iMessage suddenly thinks his Samsung SMS address is an invalid iMessage number. When I type his number on the new message bar and either send a message, it shows up as blue instead of green. He does not have iPhone and never did. I did turn on and off iMessage, reset network setting. How do I clear this condition on his number and set her up as SMS? It is so weird that this occurred without either of us doing anything. I did delete his cell number from my contacts and re-entered it, thinking that might help but it did not. Ideas???