Mystic Theurge: Druid / Wizard build: What happens with the animal compaion?

[Ezzard]

So I've been looking into Mystic Theurge out of nostalgia. And I've come to realize that I could make a Druid/Wizard build instead of a Cleric/Wizard build.

I know that if you are specialist wizard you still gain a specialist slot leveling up as a mystic theurge. Does that also mean that the druid's animal companion levels up accordingly? Granted even with Boon Companion it will still be 3 levels behind the caster at level 20. But it would still be better than being 13 levels behind.

[zza ni]

the pecelist slot is from the spell caster level ups. and that is increased by the prestige class. but the animal companian has no such increase so it stays at the druid level (with +4 up to hd if usin boon companian)

[Ryze Kuja]

Negatory, unfortunately. The animal companion will only level up when you put levels into Druid, not Mystic Theurge :(