Twilight Incident

The Twilight Incident was a conflict that took place in Ben 10: Ultimate Hero, where in the original timeline, Ben Tennyson suffered memory loss when parasites from a temporal void entered his mind due to them being attracted to the energy from the Omnitrix.

Prelude
Near the end of the events that took place in the Alien Force episode: The Final Battle. Ben Tennyson was able to escape from Vilgax's ship just as it exploded inside the ocean. After Ben reunited with Gwen, Kevin, and Max, Ben was rendered unconscious due to the presence of the parasites.

Ben was taken to Galvan Mark ll, where Azmuth discovered the parasites inhibiting Ben's brain. When Ben regained consciousness, Azmuth explained the situation to him, stating that there was no cure to remove the parasites.

Some time later, Vilgax discovered that Ben's condition, and was able to escape Earth. He planned to build another ship that would be able to destroy Earth. Learning this, Gwen and Kevin set out to stop him. But Ben protested, saying that despite his condition, he still wants to stop Vilgax. The trio pursued Vilgax using Kevin's new ship, the Rustbucket 3. They eventually found the location where Vilgax's ship was being constructed, but the conqueror had already left straight for Earth.

Destruction of Earth
When the trio reached Earth. They were horrified to see Vilgax's ship obliterating the entire planet with its power weapons. Earth exploded into massive chunks. With humanity practically gone, the gang retreated to Galvan Mark ll. Azmuth deemed Ben incapable of using the Ultimatrix, despite Ben pleas.

A New World
With help from the Plumbers, Ben, Gwen, and Kevin and what was left of humanity traveled to a remote solar system that contained an Earth-like planet for the people to settle on. After a settlement was formed on the surface, Gwen took care of Ben while Kevin left in order to figure out a way to cure him from his condition.

Nine years later, after Gwen explained the events that transpired to Ben. Kevin arrived, stating that he constructed a device that would remove the parasites one cluster at a time. Ben asks why couldn't the parasites be removed all at once. Kevin responds, saying that it would be best if they took things more slowly for his safety.

Discovery
After one cluster is removed. Kevin examines the readings he took before and after the procedure, and notices that the group of parasites are removed in both readings. Seeing how the parasites exist outside of normal space, they gang comes to the conclusion that if all of the parasites are removed, history could be altered to where Ben could never be infected in the first place. After they make this discovery, Vilgax's fleet arrives in orbit above the human colony. Realizing they are out of options, Kevin rushes to complete the procedure by removing all of the parasites from Ben.

Aftermath
With the parasites removed, the timeline changed, causing the parasites to never exist in the first place. But as a result of the forced removal of the parasites, Ben was thrown into the temporal void and received injuries that severely disfigured him. Wandering aimlessly, Ben put the blame on Professor Paradox, seeing him as the one who could of prevented the events that unfolded. Ben was able to reverse his age back to 16 years, seeing how he was a teenager in a adult body. He then found out that history changed, figured out how to communicate with others in normal space, made himself known as Envoy, and used Albedo and Psyphon as pawns in order to attract the attention of Professor Paradox so he could move his injuries over to him.