Charlemagne's Twelve Paladins

The knights of Charlemagne (Charles the Great) who Astolfo served under, for which only the most excellent people were selected to join. They are similar to the Knights of the Round Table in King Arthur's legend, and the number and members of the Paladins differ depending on the documents which reference them. Among these uncertainties, Astolfo is also definitely confirmed to be one of the Paladins, and other members such as Roland, famed for being the wielder of Durandal, and Oliver, who wielded Hauteclaire, boast of great popularity and renown.
Roland felt in love with a beautiful queen known as Angelica, but due to being a proud woman, she rejected the idea of falling in love with a mere soldier and eloping with him, and so Roland went mad, throwing off all his clothes as he began rampaging around while completely naked. Concerned for him, Astolfo and the other Paladins worked hard to capture him and gave him a bottle of reason brought from the moon, thereby restoring his sanity. Astolfo's current appearance is connected to how he dressed up as a girl during this episode.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia