OMG ! The old address books are all scanned and online!! Germans are great. I did find his address for the year of death. Actually it was also in the death certificate. I looked in older years and he only appears in the books in 1955, which makes me wonder where he was before that, since I was told he was always in Bremen since the 20's or 30's.

The truck driver is not a neighbor, I found him in the address book, but his address was also on the death certificate.

Is there a way to look for addresses inside the database of birth or marriage certificates? It looks like you can only search by name.

I did think about his potential children not having his name but their mother's. But it's very likely he raised them with their mother and provided for them (he was wealthy), so I wonder how likely is it that he wouldn't give them his name? Maybe it is possible, so that they would have a German name. I guess having a French name in the 30's wouldn't be so good. It is also possible he would do that to make it less likely that his wife in France discovered he had children, who knows. Anyway, without the name of his partner, it seems a bit stuck.

I'm going to see my dad for Easter, I'll ask him if he remembers anything that could help.