Bob becoming King after removing the Sword in the Stone is a clear reference to the Arthurian legend, and the weapon seen here bears some resemblance to the version seen in the 1963 Disney film. That's not the only cool thing about the Sword though; it's exactly same as one owned by the Minions previous master. The sequence detailing it isn't in the movie itself, but can be seen in the third trailer; at some point in the Middle Ages they inadvertently impale their then master, a King, with a sword that has the same jewelled hilt as the one in the stone. It's possible the vignette was cut so the similarity in design of the past and near-present swords weren't noticed - that would be implying King Arthur was a baddie after all.
