......

explain

He shaves his head - another way of hiding potential Valyrian-genetic traits.

He shows signs of loyalty to the Targaryens in the epilogue despite Kevan formulating a plan to promote peace across Westeros

which is out of character with his traditionally neutral stance and position.

He was trusted by Mad Aerys in the period where he earned that nickname - a period where he was paranoid about usurpers.

Varys also sounds like a Valyrian-styled name. Or Targaryen, though they may be one in the same. There's only one other Valyrian noble house in Westeros and we don't see much of them.

Oooo

I googled it and apparently people are speculating he could be descended from a Blackfyre from across the Narrow Sea, which lines up with his background from what we know.