Just use common sense. If you mean, how most likely is, the anime episode where GB was confirmed to have a regular blade and that King and Queen were actually injured then you didn't even need to watch the anime to know that. There could have been some confusion about the black blade since in the manga it seemed black, yet since nobody said anything about it and since GB doesn't even seen a swordsman (he also never used it despite being chased out of Wano) it was easy to predict how that was gonna end. Also if you are the only one beside Mihawk and Ryuma to have a black blade in the whole manga Shanks wouldn't have destroyed him to that degree.