The Brits got a very fortunate torpedo shot and hit the rudders of Bismarck jamming them in the process.
She was a sitting duck for KGV and Rodney when they arrived.
A lucky shot indeed. Had the Bismarck not been slowed down sufficiently, she would have easily outrun the surface ships and made port.
What neutral Spain would have done in that case would've been an entirely different matter for speculation.