「神{かみ}のみぞ知{し}るセカイ」 is the title of a manga/anime series but I'm not asking about the anime. I'm just curious about the 「ぞ」 part in the title.
I know there is a ぞ particle that is similar to よ, such that 行{い}くぞ is similar to 行くよ. But I have never encountered よ nor ぞ in the middle of a sentence/clause before, so this made me curious.
Which part of speech is that ぞ? What connotation does it bring and how do we use it in a sentence?
p/s: I know the ぞ is not a part of のみぞ because when I entered のみぞ in my Japanese dictionary software it only returned のみ = “only" so I deduced that the ぞ is a separate word.