Hello!
After I saw lampo's pictures of the unpollinated 'Sao Luis' - and the leafs, too - I'm about 90% sure that we have a match! :-)))
Being an non-pollinated fruit might explain why the taste is somewhat "boring", too! (Am I right in this point?)
Thank you ALL!! Thank you the most, Francisco! :-)
And thank you, too, Eli! :-) The link to the pdf was interesting, I give the remaining 10% "sureness" for the ID to 'Zingarello nero' (means that little black cigar??)
Greetings, Kai