A close friend and I were wondering, if a Magus/Wizard share a spell from both of their spell lists, how it is cast in regards to usage and preparation. Say, a Magus has a spell in their Wizard spellbook. Can it be prepared and cast as a Magus spell?
Here's a relevant quote:
"A magus can learn spells from a wizard’s spellbook, just as a wizard can from a magus’s spellbook. The spells learned must be on the magus spell list, as normal. An alchemist can learn formulae from a magus’s spellbook, if the spells are also on the alchemist spell list. A magus cannot learn spells from an alchemist." -Pathfinder Advanced Player's Guide