With all the signs pointing theories in the direction of Blackbeard being the son of Rocks D. Xebec, I figured I’d toss another idea in the mix.
What if Shanks is the son of Xebec?
Shanks is 39, he would have been an infant during the God Valley Incident which took place 38 years ago.
We know that Garp does not like to talk about the God Valley Incident. What if part of the reason was that he discovered Shanks there? He killed Rocks alongside Roger, and the two of them then find infant Shanks on Xebec’s ship.
Knowing that the World Government would not accept a child of Rocks D. Xebec into the world, Garp knew that only choice was to either leave him to die or let Roger take him with his crew. This is how Shanks came onto Roger’s ship to be an apprentice.
Another important piece: This would further solidify why Roger entrusted Ace to Garp. Because of the God Valley Incident and Shanks, Roger knew that Garp would not allow a child of a pirate to be imprisoned/killed by the World Government.
A twist like this would be insane. I guess we’ll just have to wait until Oda reveals Xebec’s hair color to be red, right?
*Theory by Team_Sanji