。
As it happens, I do know him.
Literal
Coincidentally-[even-にも] I [topic-は] him [object-を] know-[resulting state-ている][feminine-の].
偶然にも 'as it happens, coincidentally' uses the combination 偶然 'chance' + にも, which adds mild emphasis ('even by chance / as it so happens'). 知っている is the resulting-state ~ている form of 知る 'come to know'; Japanese uses 知っている for 'know (already),' not bare 知る. The sentence-final の gives the statement a slightly feminine or intimate tone, as if confessing a connection.