maybe so ...but a vassel
did'nt he attack Paris and take it more than once and king Henri was no friend either
You misunderstand how feudalism works. He held the dukedom of Normandy under the authority of the french king, but this didn't make conflict between the two unlikely. Remember the early Plantagenet Kings had to do homage to the french king for the likes of Aquitaine and Poitou but that didn't stop them going to war against each other either