B♭ isn't the relative minor of C♯? I think that'd be A♯ minor.
Edit: Actually B♭ minor is the enharmonic equivalent of A♯ minor. IE another case of things in music that are the same but aren't.
Edit: Actually B♭ minor is the enharmonic equivalent of A♯ minor. IE another case of things in music that are the same but aren't.
slowly backs away
And now I'm down the rabbit hole of reading about tuning systems again.