Fans of the DC Universe know that Connor Hawke of Green Arrow fame will make his debut in the upcoming "Legends of Tomorrow" set for premiereing in January 2016. However, his history and parentage will be a bit clearer in the crossover episodes of his supposed father's "Arrow" and "The Flash".
We say supposed because according to the comic books, Green Arrow is Oliver Queen's (Stephen Amell) son, but we have learnd that in the series he will be an African-American youth who is not biologically related to Oliver. We do, however, know that Oliver does have a son, and most of us had imagined that he would be the one that grew up to be the Green Arrow.
In Season 2 Episode 27 of "Arrow" titled "Seeing Red" we learned that Oliver had made a girlfriend pregnant long ago, and that Moira (Susanna Thompson) had "taken care" of it. The topic was not addressed until Season 3 cross-over episode "Flash Vs Arrow", in which Oliver ran into the girlfriend.
Although she did not mention anything regarding the pregnancy, the girlfriend expressed her condolence at Moira's death, adding that, "She loved you very much", possibly alluding to the efforts she took to hide the pregnancy from Oliver. At the end of the scene, we see her telling on the phone, "Mommy will be home soon", suggesting that the mother and son are possibly living in Central City.
Since then, "Arrow" has not referenced Oliver's illegitimate child, but in the upcoming cross-over "Legends of Today" and "Legends of Yesterday" Barry (Grant Gustin) will inform Oliver about his son. In a sneak peak, we also see Oliver at his ex-girlfriend's doorsteps and telling her, "I know William is my son".
So we do know for a fact that William is not the Green Arrow, and the Green Arrow of "Legends of Tomorrow" is not Oliver's son. But one mystery still remains unclear; who is Oliver talking to in the grave in the Season 4 premiere episode?
Our guess is that it would be Captain Lance (Paul Blackthorne), who has had a pretty huge arc in the current season. He has been an asset to Team Arrow, by being a double agent for them while pretending to help Damian Darhk (Neal McDonough), the Big Bad of Season 4.
It is only logical that the HIVE leader kills him on finding out about the truth, and Oliver's apparent depression is warranted, seeing as he holds responsibility for the death of someone he looked up to. There are fan theories that suggest that it could also be his daughter and the Black Canary Laurel (Katie Cassidy), whose death Damian could chalk up to retaliation to Lance's disloyalty.