The most interesting thing about the 1965 Kadett is that it donated parts to the Opel GT. And even more interesting is the 1968 Opel GT was made in France by Brisonneau and Lotz in Creil.
Eight versions of the Kadett could be had: four door saloon, two door saloon, two door fastback, four door fastback, a two and four door estate and two variants, one known in German as a Kiemencoupé and the other the LS coupé.
The Kadett has a fair amount in common with the themes of the Dipolmat/Kapitan/Admiral saloons (1964) and Rekord B but scaled down. It appears to have kicked off the series of Buick-inspired Opels which drew their inspiration from the 1963 Buick Riviera.
Making sense of the timing is the fact that the Rekord B was designed in the US and had stylistic links to the Chevy II. Presumably designers from the various studios were free to wander around and look at what each other were up to.