Congratulations! Sounds like you got a helluva upgrade with the new job. If your boss had been a pain to you, I’d personally just tell him now and ruin his weekend, but I’m obviously not as decent a person as you. 
I think I may send the letter tomorrow afternoon. I want to clear my personal stuff out and get my files off of my laptop before I do anything.
He recently wrote and sent a recommendation letter to a university I’m applying to. He can’t revoke that, can he?
ETA: Thanks again everyone!