The last episode of Boruto: Naruto Next Generations adapted one of the last Naruto stories Masashi Kishimoto wrote himself, Naruto Gaiden: The Road Illuminated by the Full Moon, and with it brought a heavy reveal for Mitsuki.
Although it has been confirmed in the past that Mitsuki was indeed Orochimaru's son, this episode revealed that Mitsuki is not only a creation with enhanced power, but not even the first one in the line.
In the episode, Mitsuki wakes up and finds himself under Orochimaru's care. Having lost his memories, Orochimaru tells him he had previously failed a mission attempting to take down a mysterious ninja named Log. But during the mission, he soon discovers that Log is actually an older Mitsuki.
"Log" then tells Mistuki that he is the latest in a line of attempts from Orochimaru to create a strong warrior, and that he is trying to save Mitsuki from sharing his fate as well. Orochimaru then confronts Mitsuki and tells him to choose between helping "Log" or continuing to follow Orochimaru's orders.
But Mitsuki is so angered by this betrayal he activates a secret power within him, an ability to reach Sage Mode (just as Naruto was able to do in the original series). With this Sage Mode power, Mitsuki instead decides to forge his own path away from both Orochimaru and the older Mitsuki.
But it turned out that Orochimaru was merely testing Mitsuki to try and get him to activate the Sage Mode power on his own. Mitsuki may be Orochimaru's creation, but Orochimaru has no intention of raising a mindless soldier. Thinking of Mitsuki as his son, as was demonstrated at the parent-teach conferences at the ninja academy, Orochimaru is indeed proud that Mitsuki has reached a point were he can make his own decisions.
For those unfamiliar with Naruto, it has quite a storied history. Originally created by Masashi Kishimoto, the series ran in Shueisha's Weekly Shonen Jump for 700 chapters. The story follows Naruto, a young ninja with a sealed demon within him that wishes to become the leader of his home village. The sequel, Boruto: Naruto Next Generations is set several years after the events of the original Naruto story and featuring the children of many of its key characters such as Naruto and Hinata.