How do I tell this guy my period came earlier?

Sooo... I have plans to meet with this guy on Saturday (this Saturday) but my period came early, way earlier than I anticipated. How do I tell him??

We had planned this day for almost a month and I feel really bad, but we’re not a bf/gf relationship so I feel really weird to tell, I don’t know how he will feel about it.

Any advice on what I could say?

Update: yes it very much is a sex related question 😏

Update 2: I told him and he was super sweet about it, thank you guys for your advice! For those of you who said that it’s not right to feel comfortable having sex with someone but not about telling them about your period, I totally see that but I was brought up thinking that menstruation is something you don’t talk about with men, I know it’s messed up, and even though I try somethings stick with you 🤷‍♀️ but I’m really glad I told him, thanks again for all the advice