This is a case of what's commonly known in linguistics as "folk etymology". You're making a connection that on the surface works, but has no... real... etymological basis.
Both the "real" and "royal" are Latin words that English took either from the Norman language or maybe later on from French. These derive from two unrelated Latin roots.
The first one is from "realis", which in turn derives from "res", literally: "a physical thing". And ultimately, from an Indoeuropean root meaning "goods, wealth".
The second one derives from "regalis", which in turn derives from "rex", "a king". This is the same Indoeuropean root found in English "right", German "Reich" or Hindi "Raj". Its general meaning is "to straighten, to rule" (both words derive from it, incidentally, so we're defining the word using the same word...)
In both cases, the "-alis" suffix forms adjectives meaning "related to". So, "thing-ly" and "king-ly", if you want...
The fact that in Castillian both roots have ended up converging is due to simple phonological developments and has no bearing on French, or English that would take up too much space but are perfectly documented and easy to explain.
So, I'm afraid the connection you're trying to make isn't... really... there.
A more substantial one would be the fact that the we identify "truth" with "material", and "rule" with "straight...