The sentence in question is
For me, this would mean something like
"In any case, there is no doubt it was hiding its mighty power." (a)
However, Google translate gives the following sentence:
"In any case, there is no doubt that he had a great power." (b)
Now, normally, I don't take stuff from Google translate at face value but in this case, I've seen other people translating this sentence both ways (both (a) and (b)).
Context-wise, the sentence appears as part of the following dialogue,
and it translation (b) can fit too. According to Jisho though, 秘める only has the meaning "to hide".
That being said, is (a) the correct translation? Is (b) possible as well?