According to chapter 957, Rocks D. Xebec was one of the first people whom had a name featuring the “D.” Initial. Blackbeard is known as the one and only Marshall D. Teach. My theory is that Blackbeard is Rocks D. Xebec’s son.
Blackbeard has a strong belief in fate and the dreams of men, truly taking the concept to heart. Seeing how he is 40 years old and Rocks died 38 years ago, should Rocks have been his father, his death would leave the two year old Blackbeard on his own, which would be in line with the depiciton of a poor kid Blackbeard that Oda released previously.
The theory works in a very simplistic manner. Rocks had a 2 year old son (Blackbeard) when he died, and Blackbeard believing the dreams of men never end wasn’t just a reference to his own will but to the overall dream of his father, Rocks, and the passing of their will via the D. inital.
Details that support this are slowly appearing:
For starters, Blackbeard has displayed a similar hunger for world domination and terrorist approach to power acquisition as Rocks and in turn could be living similar to him as that is what is necessary for such a dream.
Secondly, Rocks collected all of the Rocks Pirates on Beehive Island. Beehive Island is now currently occupied, and owned by the Blackbeard Pirates. Blackbeard could be occupying such an island due to his familiar connection.