The wingspan was about 3cm.
No interactions present.
I have now checked against P. secundaria, but it appears to be rhomboidaria. See www.lepiforum.de
In UK the September date of the sighting would suggest Willow Beauty which has a partial second generation in September whilst P secundaria flies July and August and A repandata flies June - July. However, in Germany the flight periods may be different.
Shape of the cross lines on the forewing suggest P rhomboidaria(second one starting at 2/3 way along leading edge is a bit faint but on the left wing can be seen to have a strong kink near the leading edge and forms a black spot on each vein).
It would be nice to be able to see underside features and shape of antennae (if male) to provide further support of the ID. In particular P rhomboidaria has a usually conspicuous pale apical tip to the underside of the forewing which P secundaria lacks.
Apologies for the Mottled Beauty ID...should have looked more closely! I also had noticed the observer's name and assumed this was from Scotland!
Probably a Willow Beauty, then, but much more colourful than I am used to, and with a very Mottled-like, blotchy, cross bar.
My Flickr photos...
Lat/Lng: 48.4, 8.0