From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Vegeta Junior's true heritage was never revealed, therefore it is unknown whether he was descended through Trunks Brief or Bra Brief. Akira Toriyama simply stated in an interview in the Dragon Ball GT: Pāfekuto Fairu that Vegeta Junior was a descendent of Vegeta and Bulma.
Dragon Ball GT
Vegeta Junior appeared in "Until We Meet Again...". He was Son Goku Jr.'s opponent in the Tenkaichi Tournament. The results of their match was never revealed, but both were seen to have the ability to become Super Saiyans despite the claim that no one with less than a quarter-Saiyan heritage could achieve the form. Even though Vegeta Junior was only seen for a moment in the series, his personality was reminiscent of his ancestor Vegeta (Vegeta Junior's reaction to Goku Junior's Super Saiyan transformation was reminiscent of Vegeta's reaction to the Multi-Form technique he witnessed during the Saiyan Saga when he said, "Hey, that's pretty cool"). He also strongly resembled Vegeta down to his upright standing hairstyle and widow's peak.
- Ki Blast – Although he is not shown using this, there is no seeing why he does not know how to use it. This is because when Goku Jr. turns Super Saiyan in Dragon Ball GT: A Hero's Legacy, he immediately masters the technique and since Vegeta Jr. can also turn Super Saiyan, then there is no seeing that he cannot use it either.
Vegeta Junior used this form against Goku Junior in the Tenkaichi Tournament. He appeared exactly the same as Vegeta did when he turned into a Super Saiyan, his hair not changing shape, but the color going blond and having a more pronounced aura, and his eyes turning blue-green.