Dragon in Exclusion

Beelzebub, Dragon Master loses complete connection with the young wizard John Lewis when he and his cousin witch Sybil Robinson time-travel again. That is because they travel to a future world that is recovering after the Robot Wars. John and his cousin Sybil, get internal computer chips, artificial intelligence, avatars and some weapons. When the two cousins return to the standing stones, the young wizard tells Beelzebub that he is now excluded from most of his brain.

When John and his cousin Sybil return from a series of adventures, the young wizard tells Beelzebub that he is now excluded from most of his brain.

They don't tell Beelzebub that they met some members of their bloodline who realised that some mysterious force is looking for Excalibur.  John has been persuaded by his future cousins to go back in time to search for the magical sword. John keeps this information secret from the Dragon Master.