I know that も particle can be used in place of は、が、を. And it means "in addition", "also".
What function does it have in this adverb "不運にも"? Should we treat it as a separate word here?
『中上級を教える人のための日本語文法ハンドブック』 explains the expression
Some adjectives like
For example, the sentense
expresses indirectly that the speaker did not expect that he would show up. This unexpectedness is not the main topic of this sentence, but a kind of commentary from the speaker's point of view.
Here is another example:
Perhaps other examples would make it more clear:
Another example of
This will always be in the form ～にも～ない or ～にも～ず.
And yet another example is when lining things up (列挙)
There are perhaps other examples of the usage also not mentioned above.