Suppose I have a rogue facing an enemy spell-caster. My rogue drinks a potion of invisibility, stealths behind the caster, and readies an action to attack when the caster casts a spell. The caster obligingly casts a spell without casting defensively, as he doesn't know the rogue is present, which would normally draw an attack of opportunity. My rogue attacks and interrupts the spell, but does he attack once or twice?
Can a character get a readied action and an attack of opportunity that is triggered by the same action?