Defeat the Final Boss for the second time while on True Vault Hunter Mode. It's level should rise to 50, if it wasn't already. If that doesn't do it, for whatever reason, kill it a third time. Yeah, it's that simple o.o --- Spell card! Diamond Will ~ Unbreakable Determination!
Save and quit. Reload and presto level 50's. --- The Queen of Light took her bow, and then she turned to go. The Prince of Peace embraced the gloom, and walked the night alone.-Battle of Evermore/Zeppelin