It is a Goliath GP 700 Sport from 1951. The car body is made by Rometsch, Berlin.
Only 25 Coupes have been made. 700ccm, 24 PS and 110 km/h for DM 9.700,-
My grandfather used to have a Borgward and it was not the only "exotic/uncommon" car he had 
Dirk, I wish you and your family all the best!
Oliver