Damian Wayne revealed!

K.F. returns with Who?

It was during Tim's time as the Young Justice Leagues' Robin.

He still questions most of the things he had bore witness to at the time but the undeniable truth was right in front of him now.
As well as a matching DNA test he had conducted himself thrice to validate the person.

Truth be told, Dick, Tim and Bruce had heard of Damian's existence before meeting him a few months prior and the difference in personality was striking to both Bruce and the time they'd met him before Talia came to drop him off with them.

How it happened? you may ask.

Easy, one day in Mt. Justice where he was relaxing in the lounge, working on his computer with a cup of coffee, an earthquake had suddenly shook the entire mountain. In the process his computer got fried by the mug toppling over it, ruining not only his lifeblood (coffee) but also his best friend, the computer.

He cursed, going to investigate the quakes origin. Mt. Justice was safe against most natural disasters and had a lockdown mode.
They could be hit with a Point 10 Earthquake or Tsunami and the place would still be standing.
He also doubted it had been any of the others as this was their agreed-upon chill-time.
If anything, he'd have heard the oven explode before an earthquake occured.
Though that statement would be invalid if he were in Gotham, where everything was possible.

Arriving near the main area he found something that distinctly reminded him of the time Impulse had appeared.
An electromagnetic energy field, whose power was being discharged into the surrounding area as a means to stabilise itself in space-time, was there.

He called the others to greet the invader and possible second time traveler. They gathered within the next 3-7 minutes.

Just when most had arrived the lightning bolts gathered and struck one spot, causing a cloud of dust and light to blind them.

"So, is this your correct timeline?" drawled a deep, baritone voice that not only sounded tired and annoyed but also had an eerie resemblance to Bruce's I'm surrounded by Idiots™ mood.

The voice sounded like him too, he noted at the same time.

"I think so... we're in Mt. Justice and it looks just like when I had lived here" intoned a decidedly much younger and more excited sounding male. This one also reminded the team of someone. Though not of a Leaguer but someone from the past. A painful memory echoed in their heads, making them queasy.

Nightwing gasped, a premonition appearing in his stomach as heavy as rocks.

It couldn't be.. right?

The dust settled and there were two people. The team gulped.

Their eyes darted to the bigger threat: the undoubtedly older one with the deeper voice, who was not just tall as all hell but also dressed in a black suit (which had an uncanny resemblance to Batman's.)
And the overall resemblance didn't just end with the suit; his built, even his stance overlapped with Batman's, which Dick and Tim noticed almost immediately. The two bats looked at each other in trepidation. A clone?

The other was___

".... Wally?" Dick choked up on his saliva, tears brimming in his bright blue eyes. Robin gasped, then looked between the groups, clearly shocked.

"Dick!!..." The boy screamed, jovial, as he looked towards the speaker. His face drew a blank. "Wait, who are you?"

The Batman-ripoff sighed. "West, that's Nightwing, the future persona Grayson assumed after his time as Robin."