I would assume that is the secret one.
from what it seems there are 2 ways for how this can end, diplomatically... and not diplomatically.
of course your actions during the journey will decide if even both options will be open to you.
the diplomatic one likely is the secret one, givne what is needed for it.
in comparison to the other one.
(and yeah I talk super vague on purpose cause dont wanna spoiler stuff. but from what i see, there basically are these 2 endings, assuming the dev doesnt reveal a third one. which Iowuld have no clue how or where to obtain)