What would happen if you cast Simulacrum on a shapechanger?

While there are many kinds of shapechangers in the D&D universe, such as vampires, lycanthropes (all of them), imps, doppelganger and channelings, there isn’t much said about how they interact with the Simulacrum spell.

The Simulacrum spell states:

You shape an illusory duplicate of one beast or humanoid that is within range for the entire casting time of the spell. The duplicate is a creature, partially real and formed from ice or snow, and it can take actions and otherwise be affected as a normal creature. It appears to be the same as the original, but it has half the creature’s hit point maximum and is formed without any equipment. Otherwise, the illusion uses all the statistics of the creature it duplicates, except that it is a construct. […]

Does this mean that a polymorphed being (be it from spell, curse or natural ability) would be copied in their current form? or would their "true form" immerge in the snow?

I can see this being quite useful either way:

  • Your party’s changeling studies and creates a persona of the king or an important person, then you create a simulacrum of the changeling king. Now you have 2 or 3 walking talking kings to create all sorts of chaos.
  • Though it would take 12 hours, if Simulacrum would reveal a true form, one could easily prove who is the real king by simulacruming one of the copies.