He has/had a relationship with Anna - Annie Gers.
Pauline Berens: Genealogienetwerk zus Greetje Berens voorheen EemslandBoekweitBoerenImmigratie
https://www.genealogieonline.nl/the-dutch-connection/I53921.php
ouders: Charles Theodore Keller 20 May 1850 Munich - 22 Dec 1912
Cincinnati, Louisa Van Leeuwe Keller 7 Aug 1855 Cincinnati - 13 Nov 1906 Cincinnati
https://www.findagrave.com/memorial/52724904/charles-theodore-keller
https://www.findagrave.com/memorial/144944357/louisa-keller