How best to let a hiring manager down?

I've seen a few posts on here recently about going through PECs/having accepted a provisional or formal offer, then being offered a better job elsewhere and accepting it. From what I've read, this is fine to do (if frustrating for the original hiring manager). My question for people who've been in this situation before is how have you informed the original hiring manager that you've received, and plan to accept/have accepted another job offer? What did you say in the (I assume) email? Did you set up a teams meeting to discuss it at all?