Hello Rich, I have a pic with my uncle on my dad's Horex Regina taken about the same time that your pic was shot. Seems that boy's footwear at this time was Espandrilles When my dad was sleeping during daylight hours due to his nightshift, my uncle would 'borrow' the bike and ride it through town.... (age 13) Not for long though. My dad was not amused.
lol Winglad. Looking at the photo again, and knowing that reg was from 1958, I reckon that was one of the very first 99 Dommies and taken in 1958/59.