They were in the same graduating class from Hogwarts. Pastmaster kept manipulating time to keep Mumm-Ra from finishing his final exams within the anointed amount of time so that explains why Mumm-Ra can't stand cats.
"Say goodbye to the universe, Maximals! The future has changed. Yessssss. The Autobots lose, evil triumphs, and you... YOU! NO LONGER EXIST!" - Megatron declares ENDGAME!!! (Beast Wars, The Agenda: Part III)