There are lots of Robert Frank Millers and Frank Robert Millers. Familysearch.org shows over 60 by that name or a very similar name.
To have enough information to answer your question, could you please provide his birth year and what country, county and or city he was born in? The same kind of information on his marriage, the year and the location would also be useful.
Familysearch.org only shows information on deceased people and they have extensive information.