It's the nostr:npub1s3ht77dq4zqnya8vjun5jp3p44pr794ru36d0ltxu65chljw8xjqd975wz "social" relay. You're on it, which is why I can see you.
Discussion
Oh yes 😂 I see now that i've previously added it to my relay list, and also that it's a paid relay which I suppose means I must have already paid? Guess that shows how long I've been afk if I've forgotten these things 😂