In You've Got Yale!, it become obvious quickly that Jack is failing at his job and the company is suffering as a result. Still angry at being outed by Jack, Chuck attempts several things (buying from the black market on his credit card, getting him on Megan's List, considered crashing Jack on the Bass Industries jet) to prove Jack is unfit for the job but fails each time. He turns to Lily van der Woodsen for help but each are unable to come up with a suitable idea. At the opera that evening, Lily realizes that since she was planning to legally adopt Chuck while Bart was still alive, she still can. That enables her to retain controlling interest of the company until Chuck turns 18 (and, in essence, allows him to run it before then). After Chuck signs the papers, which Jack witnesses, he confronts Lily while high and attempts to angrily rape her. However, Chuck gets there before anything happens and physically restrains him. After that, he's sent back to Sydney.In The Goodbye Gossip Girl, in Gossip Girl's tell all blast, Chuck finds out Blair slept with Jack. How to Succeed in Baseness, Blair calls Jack to expedite Chuck's liquor license so they can open the club at The Empire sooner. Chuck finds out and is angry since Jack is the last person he would ever call for help. Afterwards, Jack sends her flowers with a note stating the license was fake. Blair and Chuck allow the police to end the party before Jack can to maximize their publicity for potential future clients.
Jack returns in The Sixteen Year Old Virgin after Chuck's biological mother Elizabeth Fisher reveals herself and begins building a relationship with Chuck, and after Chuck is confronted with a sexual harassment lawsuit. Jack begins to instill doubt in Chuck about Elizabeth's legitimacy: saying he saw her dead body at the funeral viewing, that he and Elizabeth never got along, etc. Chuck begins to believe him and conducts a DNA test on her and finds out she really is his mother. At the same time, Chuck's lawyer is encouraging him to sign over ownership of The Empire to a family member, and he decides to ask Elizabeth who hesitantly accepts it. In The Empire Strikes Jack, it's revealed that everything that happened was all an elaborate scheme thought up by Jack to take The Empire from Chuck. Elizabeth also reveals that she's in love with Jack because deep down he's a loving and caring man, although Chuck warns her that Jack is incapable of love and no caring man would convince her to participate in the scheme. Afterwards, she breaks up with Jack and leaves him to live out the rest of the scheme alone. In Inglourious Bassterds, Chuck meets with Jack to see if there's any way to get The Empire back. While shopping with Serena van der Woodsen, Blair runs into Jack. He sees her looking at a gown and mentions how beautiful it would look on her. Angry, Blair asks how his meeting with Chuck meant. Jack reveals that he told Chuck he could have The Empire back if Blair can spend a night with Jack. He later sends her the same dress from the store, along with a note saying it was her last chance to save Chuck. Blair, after seeing how sad Chuck is, decides to do it. When she arrives, she gives Jack a contract to sign, which states that he must sell The Empire back to Chuck (to dispel any suspicions) and leave town. He signs and kisses her. Blair is eager to get everything over with, but Jack instead informs her that Chuck knew about the deal and set it up. He explains that he was the one who paid for the dress and knew what strings to pull to get Blair with Jack. Upset, Blair goes home and finds Chuck. The two argue and subsequently break up. At the end of the episode, Chuck returns to The Empire and Jack leaves to go back to Sydney.War at the Roses, Dan Humphrey tries to spread a rumor that Blair and Jack spent time over the summer together and are planning on hooking up again, to ruin Blair and Chuck's newfound amnesty. It fails, but Chuck feels something is up when Blair knows exactly where Jack was all summer. At her birthday party that evening, Blair reveals that she only knew where Jack was because she was desperate to find news about Chuck but only found info on Jack. At the end of The Townie, Chuck leaves to find Jack to try and take Bass Industries back from Lily, who he thinks has betrayed him by attempting to sell Bass Industries. In Shattered Bass, Jack returns to New York after Bass enemy Russell Thorpe's daughter Raina Thorpe invites him to help her take down Chuck. After meeting with her, he decides she's too immature and decides to pair with Russell, who promises him good compensation if he succeeds in taking down Chuck. Later, he goes to see Chuck at the site of his new hotel. He arrives with some medics from a mental facility and announces Chuck is going to rehab. Angry, Chuck punches Jack in the face and the men, along with Nate Archibald, escort Chuck out of the building. Jack makes eye contact with Russell, who was watching from the wings and leaves him a key to Chuck's suite at The Empire and tells him to take anything he wants. After collecting what he wanted from the suite, Russell is leaving when he's met by Jack, Chuck, and Nate. The three reveal Jack played double agent and was never going to send Chuck to a mental facility. They watch the security tape Russell stole, which reveals that he killed his wife, Avery Thorpe, not Bart, as he claimed. Jack goes to call the cops, but Chuck tells Russell they won't so long as he leaves and never comes back. Before Jack leaves to go back to Australia, he tells Chuck to fight for Blair and not lose her to someone like Louis Grimaldi and to keep the Bass legacy alive.
In Riding in Town Cars With Boys, Chuck and Blair are in a terrible car accident and Chuck loses a lot of blood and needs a family member to give him blood. In The Princess Dowry, Lily reveals to Chuck that Jack was the one who gave him blood. As a result, Chuck invites back to town in Con-Heir to dedicate a hospital wing to him as a thanks. However, Chuck begins to find flaws in Jack's story. When he questions Jack about the fact that his time in boarding school should have prevented him from donating, along with sleeping with prostitutes and doing drugs, Jack just says he lied so he could save his life. He goes to the hospital and is able to secretly access Jack's medical records where he discovers Jack has Hepatitis C and definitely not a suitable donor. He sets Jack up with a fake sick kid so Jack has to admit he can't donate blood. Chuck realizes that Jack was just covering for Elizabeth, and he admits he was.
In Salon of the Dead, Lola Rhodes, in an attempt to reveal Serena is Gossip Girl, accidentally live streams Diana Payne revealing that she's Chuck's mother. But in Despicable B, Nate realizes that Elizabeth and her actions were all a set up orchestrated by Jack. He figures that since his grandfather William van der Bilt supported her financially in the past, she needs another source of funding now. He finds out that her backing is now coming from an Australian holding company which has Jack named to the board of directors. Also, he tries unsuccessfully to reach Elizabeth. She eventually emails him a picture of herself pregnant with Chuck. He speaks of his suspicions to Chuck, who explains to Nate that the only thing Diana and Elizabeth have in common is Jack. He tells Nate to look at the tattoo on the man in the photo's arm again, and he produces a photo of himself and Jack on a beach and Jack has the same tattoo. He says that the real question is not who's his mom but who's his dad and that he thinks Jack is his father.
In Raiders of the Lost Art, Chuck, Nate, Blair, Lola, and Serena attempt to use Diana's day planner to find Jack. The planner was in code, but they break it and figure out she's going to a mysterious party that evening. Chuck figures that that's a perfect place for someone like Jack to be and they plan to go. At the party, Chuck finds Jack and finally asks once and for all if Jack is his father. Jack asks if he really wants to know, and security then escort Chuck out of the party. Meanwhile, Blair is also in the house and opens a door to find something shocking. On her way out, she runs into Jack where she demands to know if he's planning to tell Chuck what he's really hiding there. Jack tells her that there will be a lot of people who will get hurt if it ever gets out and she needs to leave immediately. Outside, Blair tells Chuck he needs to go back into the house when everyone leaves. Inside, Diana and Jack are relieved their plan can still work out after their party was crashed. But before they can make any moves, Chuck bursts in and finds them with a very much alive Bart.
In The Return of the Ring, Chuck meets Jack in Monte Carlo to get enough money to fight for the power of Bass Industries, which was taken over by Bart; who cut them both out of the company.
Jack makes his final appearance in the series finale New York, I Love You XOXO. He finds Chuck and Blair in the bed and breakfast they're hiding out at after the death of Bart. The police are looking for them to get as much info on Bart's death as possible. Jack suggests to them that if they get married, they will have spousal privilege and they decide to. Jack obtains a marriage license but they decide they want to get married with their families and friends there so they relocate to the Bethesda Fountain. Meanwhile, Jack meets Georgina Sparks and they help each other make the wedding happen without a hitch. In the time jump, it's shown that they ended up in a relationship with each other.
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