Pokemon X and Y aftermath

Takes place after the kalos league challenge, Serena, Ash, Clemont and Bonnie gets entangled within a past fued unknowingly. Serena confesses her love for Ash at last, but will her feelings be in vain? Bonnie vanishes with Luminose City; could the disappearance be linked to sightings of Yveltal and Xerneas? And who was this princess? And what was her involvement in this story?