Probably call him Dan. But yes you should ask.

Different transgender people feel different ways about this, so the advice to ask Dan is the right advice.

I would say Dan, and if needed, it’s ok to say Dan was known as Denise back then.

Ask Dan.

In my all girls high school, I knew Denise. After HS, we lost touch and reconnected over a decade later. Eventually Denise announced she was bi, then gay, then trans and going by Dan. So I now know Dan, and use he/him pronouns.

When I am telling a story about something that happened in high school, back when Dan was Denise, is it appropriate to refer to him as Denise? Or no, because dead name? Thank you. I want to be clear who I'm talking about but don't want to hurt Dan's feelings.