In the divorce counter petition of Bullough v Bullough and Nentwig, an Albert Nentwig is cited. As Bertha Bullough's petition is accepted by the judge and the counter petition unheard nothing else is known of this person. John claimed that Bertha had committed adultery with him, and it is supposed that John doubted Edward's paternity, but there is no evidence either way.
Thomas Krebs has done further research and writes (July 2012) :
'I may just have found out who Albert Nentwig was. When I first heard the name, not a very common one in German speaking countries, I Googled it and found only one person by that name who could be the one I was looking for, a doctor in Munich. In the Munich city archives I found his residence registration data: He was born in Skasov, Bohemia, on 12 October 1850, two years after Bertha. He studied medicine at the university of Munich and lived in Regensburg at the time. In Bohemia, he worked as a doctor for the poor, and in the mid-1880s he was the physician in charge of the "Wasserheilanstalt" (hydro-therapeutic clinic) at Thalkirchen near Munich. This is where Bertha's niece, Friederike (her sister Marie's only child), drowned in the river Isar in June 1893. In the 1890-91 edition of the phone book for Munich, he is listed as a specialist in nervous disorders and electro-therapy. On 12 July 1883 he was married to Luise Johanna Wurm (1864-1922) in Munich. They had one daughter, Ida Ernestine, born in September 1884. Albert Nentwig died in Munich on 8 January 1912. I don't know whether I'll ever find out more, but it doesn't seem entirely unlikely to me that this Albert Nentwig is the right one.'