"I...I don't...what?"
To say that Future Vegeta was stunned at the news which Goku had just delivered to him would be an understatement of the highest order. Sure, he had been told the old tales of Planet Sadala that were passed down by his family, and of the civil war which heralded the arrival of the Legendary Super Saiyan in a battle which tore their world asunder. Even so, he had always been told that only the "victors" of that conflict had managed to escape the planet's destruction and endure centuries of wandering the stars at the speed of light alone, until at last they found a new planet to call their own and took it by force. That there was apparently a whole other planet of Saiyans that had somehow escaped the notice of both the Frieza Force and his own people...to be frank, it defied all logic, and yet he found himself wanting it to be true more than he had ever wanted anything in his life. That this planet apparently wanted nothing to do with him...well.
That made a bit more sense, but that didn't make it any less heartbreaking.
"Why was this kept from us?" he asked first, once he had gotten over the shock enough to ask more reasonable questions than mere "hows" and "whats." Goku sighed, evidently wondering about that himself to an extent, yet also knowing that they both had an inkling of the answer.
"For their own protection," Goku replied, hoping to soften the blow as much as he could. "I'm still sorting out the details myself, but it sounds like there were a lot of people caught in the crossfire of some big conflict on this Planet Sadala: people who were oppressed by evil Saiyans, but didn't quite know what to make of this 'Legendary Super Saiyan' and his friends, either. With the planet about to blow with them still on it, they prayed to whatever god might be listening to save them in their darkest hour, and against all odds...someone answered." Future Vegeta's eyes widened: he had become increasingly aware of the true nature of the gods the longer he remained in the company of Earth's defenders, but it still amazed him to hear of such powers being exercised in an act of apparent generosity. "Of course, they knew that the bad guys probably made it out of that too, and they had spaceships, so they made a deal with the guy who got them out of there to...well, hide, pretty much. Hide in this world, serve in the next, or something like that," Goku explained, with a casualness which Future Vegeta would have thought false if it were coming from anyone else.
"Heh," he said, part of him amused at Kakarot's unflappability while the rest of him tried not to let his myriad other emotions show on his face. "And so, they distrust me on account of my birthright, not that my history would do me any favors, I imagine," he said soberly, to which Goku winced in sympathy as he continued. "Oh, but the 'Legendary Super Saiyan,' the savior of the universe, that's a whole separate matter, of course," he added, speaking less with bitterness than with the grim realization of a man who has been denied something he never knew he wanted all his life. Goku's grimace deepened, knowing that he would be forced to confirm his new friend's suspicions.
"Yeah...if it helps, King Kai tried to put in a good word for you, but that's admittedly a little complicated, what with the whole time travel thing, and-" Goku attempted to explain, only for Future Vegeta to shakily hold up a hand to stop him.
"I understand why they would see fit to bar me from ever setting foot upon their world. It is simply...disappointing, is all," Future Vegeta replied. "I tried not to think about it, but...there was a time when I believed that I was the last of our kind in my own time. To learn that this is not the case in both timelines is...a lot to take in. I have to wonder if it would have been better to let me continue to live the rest of my days in ignorance," he wondered around, leaving Goku conflicted for a minute before he finally placed a hand on the older man's shoulder as gently as he could, mindful as he was of Future Vegeta's currently weakened state.
"I knew it would be a tough pill to swallow - especially because swallowing pills is so hard, I don't know how people do it so easily! - but the point is, King Kai at least figured we deserved to know we weren't the last ones left, and luckily for us...so do they, as far as I can tell."