OK, I hope I can give you some details reasonably correctly.
This car was exhibited by Pietro Frua at the Geneva Show 1969 as "Opel Diplomat Coupé Special". Since Frua used an Opel Admiral B 2800 with the corresponding chassis number for this prototype, the car is also called the "Opel Admiral B Coupé".
The four-seater coupe on the chassis of the then new Opel KAD (Kapitän/Admiral/Diplomat) used a shortened wheelbase and the injection engine of the Diplomat.
The car was designed with official participation of Opel and was to be produced in a small series, which did not happen. Instead, another coupe design was shown a year later, together with Opel, Frua and Erich Bitter: the Opel Diplomat CD. This car was then the starting point for the Bitter CD, which came in 1973 and was produced in a small series by Erich Bitter in cooperation with Baur in Stuttgart until 1979.