I would assume so BSR. Even if you are going two base classes you can not be 18 in one and 2 in the other
Indeed, you're right; the multiclassing rules apply to all classes, PrCs included.
Does the 5 minimum prc levels still apply to unregulated prcs as well?
FYI, I never said 18-2, I said 12-8, which if you take Grimetrekker at the appropriate levels, is possible. However, it is only possible in the event that you do not become an ex-Monk and lose the ability to progress in Monk levels, because you would have to take a Grimetrekker level at level 11 to avoid the 10-level difference rule. That's why when you roll a 5 Rogue 15 Fighter build, you can't just slap Rogue at the end of it and call it a day (besides the fact that's worse for your SP pool).
I wasn't asking in reference to your specific example.
The rules state that five levels of a prc must be taken by level twenty. With three total classes it would be possible to meet the 10 apart rule while breaking the five minimum rule. Thus my question.
EO, I don't think anyone here is asking because we don't read the rules, the opposite: people are curious if the lack of regulation means some rules still apply.