I came across him while researching a paper in college on the air battle of the Ploesti oil refineries. Apparently he was of noble birth, his mother a Prussian aristocrat, his paternal line Scottish landed gentry. His full and proper designation was Douglas Pitcairn of (Scottish Placename forgotten). It's also possible that Pitcairn was the teritorial designation and not his surname. What the actual surname may be, I am not sure, tried Burkes, who track the Scottish Gentry pretty well but cannot seem to find any Pitcairns but the territory seemed to be among the holdings of the Keith family, the head of which bears the title EARL MARISCHAL. If he is indeed Douglas Keith of Pitcairn, he may be of a cadet branch of that family. He may have used Pitcairn the way Prince William registered for St. Andrews as William Wales rather than William Mountbatten-Windsor, who wouldnt. Obvioulsy raised in his mothers land and traditions he became a patriotic German officer, though I dont know to what extent he was idealogically a Nazi.
This info was in an obscure book on Ploesti I have not been able to locate since. His heritage was detailed in the context of the irony that the defending German's were just about everything but. Pitcairn commanded the Luftwaffe and the AA troops were mostly Romanian conscripts, while there was a startling preponderance of Germanic surnames among the USAAF personel involved in the raid.

I hope this is helpful

PS. I think someone above had his full name and designation as: Douglas
Pitcairn of Perthshire. Sounds right and likely landed gentry by the sounds of it, but doesnt appear in Burkes. Perhaps removed because of his ties during WWII

Also, Kaiser Bill was Queen Victoria's grandson, her husband Albert was her German first cousin, William (of orange) and Mary were first cousins who together deposed their common grandfather from the british throne. Many European wars were large scale family fueds.