Harry Styles -- Runs Into Not One, But Two Famous Exes

It's a question for the ages ... if you're going to run into two of your exes at a party, would you rather have two separate awkward encounters ... or an enormous one?

One Direction's Harry Styles chose the second option at Monday night's British Fashion Awards in London ... where he schmoozed Kendall Jenner and Cara Delevingne.

Styles was linked to Delevingne last September and Jenner just a few months later.

The scariest part for Harry ... Kendall and Cara came to the party together.

Comparing notes ... worst nightmare.