Gaston Jr. is one of the sons of Gaston and the older twin brother of Gaston the Third and also an older brother of Gil. He first appears in Isle of the Lost: A Descendants Novel and returns in the sequel, Return to the Isle of the Lost: A Descendants Novel.
Gaston Jr. and his twin Gaston the Third first appear in the prequel Novel. They are first mentioned in the prologue during Evie's 6th birthday. They are described as wrestling and balancing on top of one another much to Evie's delight. They are reunited with Evie 10 years later when she first arrives at Dragon Hall. The twins help her find Dr. Facilier's office. He and his twin fight over who opens the door to the office, however eventually Gaston Jr. wins the brawl, sending his brother down to the ground with a punch to the jaw.
After her meeting with Dr. Facilier, Evie remembers her forgotten lunch only to have the Gaston twins offer to share theirs. They take Evie on a tour of the school and introduce her to Lucifer, the school mascot. They also show her the spider that guards the Athenaeum of Evil and what the library holds. They comment that they don't care much for the library, as much the same as their father, they find books a bore.
Later, the Gaston twins appear stuffing each other into the P.E. nets and are told by Carlos to come to Mal's Hellraiser at Hell Hall or Mal will ban them from the Isle's streets.
They arrive at the Hellraiser first. After butting heads with Carlos as a greeting, they bring out pitchers of smuggled Root Beer. The boys gorge themselves with the offered food and begin to chase the Tremaine step-granddaughters around the house alongside Harriet Hook's pirate crew.
When Mal arrives, the boys stop their eating by the buffet table. They share one of Mal's Toad-blood shots and get their wallets pilfered by the fairy. They stay the night at Hell Hall, and in the morning steal Carlos's breakfast and leave.
The following day, they are seen in Yen Sid's Weird Science class at Dragon Hall. One of the twins complains that science is boring, just like the other farts. Carlos tells them and Reza to shut up. They grumble when Yen Sid comments on Carlos's half-finished science project: the Broomba.
He and his twin both appear in the sequel novel. They first appear after Mal, Evie, Carlos, and Jay walked through town. They are seen crossing a street and are greeted by Evie; however, the duo simply scowls at them and walk off.
They are among the villains that refused to join the Anti-Heroes Club.
They are next seen emerging from the Rickety Bridge alongside Ginny Gothel and Anthony Tremaine. They surround Mal and Maddy and unintentionally stop Carlos from seeing what was going on. They close in on Mal and force her to the railing of the bridge. They punch their open palms threateningly shouting "Evil lives!" in unison. When Evie, Carlos, and Jay retaliate, Jay takes on the Gastons. He runs in-between them and causes them to thump their heads together. After being defeated, they slunk away from the bridge.
- He and his twin are the only Descendants (besides Evie and Mal) to be mentioned in the prologue for Isle of the Lost: A Descendants Novel. However, he and his twin do not first appear until Chapter 3, A Beautiful Princess.
- Both he and his twin brother are enrolled in Advanced Vanities and Weird Science class at Dragon Hall.
- In the 10th episode of the School of Secrets series, Team, he and his twin were mentioned (unknowingly) at Auradon Prep when a member of the tourney team says to Chad Charming, "I wonder if Gaston has a son? That guy was ripped."