|“||The one girl here who actually appreciates how beautiful you are. You wouldn't stab me in the heart, would you, Matty Blue? No, I don't think so. You will definitely go down as the best night I never had. Oh, well.||”|
Katherine used Matt to activate Tyler's curse by a way of Matt's death; her plan failed, however, and Sarah died instead. Matt was very public with his dislike of Katherine, but protected her from Silas, along with Jeremy. After Katherine helped expel Gregor from Matt's body, the two have become allies with the possibility of becoming friends. However, after Katherine successfully possesses Elena's body, Matt goes against Katherine, once again. They share a goodbye scene in where Katherine compliments Matt before Katherine is stabbed to death by Stefan Salvatore's Traveler blade. This separates Katherine and Matt for good.
In the series finale, Katherine briefly makes a come back to try and destroy Mystic Falls. However, Matt is in on the plan that allows Bonnie to redirect hellfire to end Katherine’s life. This puts them at odds one final time before Katherine is killed for good.
Throughout The Vampires Diaries Series
In The Return, Katherine attends Richard Lockwood's funeral at the Lockwood Mansion where she talks to Matt (who believes her to be Elena). They talk about Caroline and Katherine seems entranced by his blue eyes. Katherine also mentions Matt when talking to Bonnie.
In True Lies, Katherine has been running through the woods after the car accident in the previous episode in which she left Jeremy to die, she has developed a cold and stops a car, expecting the driver to help her. However, the driver gets out to say she looks exactly like Elena before pepper-spraying Katherine as she gets her phone out, as she is one of the human's compelled by Silas to find her. As Katherine knocks the woman out and rubs her aching wrist, complaining about the pain, a shotgun is suddenly cocked and she turns to see Matt aiming the gun at her saying "not as much as this will".
Matt is binding Katherine's hands together with rope as Jeremy is on the phone with Damon. As Jeremy tells Damon that Matt is the one who found Katherine, she snarls that she should've ripped his head off when she had the chance. She then asks Matt if the ropes are really necessary, and Jeremy retorts that he left her to die, implying she isn't exactly the most trustful person. Protesting she was just defending herself against Silas, Matt asks how many people she has killed using that excuse before telling her she should be thankful they even brought her some clothes. Katherine realizes that she is the thing that everyone wants, before it dawns on her that she is "the freaking moonstone" before sitting back in the truck, clearly defeated.
After the drive to a station, they pull up to get some gas, Katherine clearly relieved to be stopping and demands that she gets out of the car to pee. Jeremy refuses to let her free, and she turns to Matt, pleading with him and he lets her out and she heads to the bathroom, looking over at Jeremy and Matt slyly as she closes the door. Matt heads into the convenience store for some medicine for Katherine when the cashier suddenly asks if the girl outside is Katherine Pierce or Elena Gilbert. Matt suddenly realizes Katherine is making a run for it.
As Katherine, Jeremy and Matt are hiding out in the woods, Matt leaves to get some firewood and is soon approached by Silas, who attempts to read his mind and compel him to keep quiet. It doesn't work due to Nadia already being inside his mind and he yells for Jeremy and Katherine to run. Silas snaps his neck and Matt wakes up, seeing Jeremy and Katherine run straight past him, ignoring him. Bonnie soon appears and tells him he is on The Other Side.
Katherine, having returned to help Jeremy against Silas bring Matt's body back to his truck and wait for him to wake up. Once he does, Katherine tells him she shot Silas and they need to move.
In Dead Man on Campus, Matt is serving drinks to Katherine at the Mystic Grill. Katherine is obviously drunk and he tries to cut her off; telling her she's starting to annoy the other customers. While replaying a video of himself transforming into Gregor, Katherine overhears and is piqued. She tells him she will help him out if he keeps pouring her drinks. She tells him a little about The Travelers and their ability to possess people.
Matt asks about Nadia and Katherine mentions she knows her. Later, Matt is led into a room where Nadia, Katherine and Stefan are. Nadia summons Gregor per her mother's request. It is revealed the dagger that is in Matt's possession is the only thing that can disperse a Traveler's essence from it's host. Katherine plunges the dagger into Matt, freeing him of Gregor's possession.
In Fifty Shades of Grayson, Katherine, fearing that her accelerated aging is dilapidating her attractiveness, has hired Matt to be her personal fitness trainer.
In The Devil Inside, Katherine, while possessing Elena's body, playfully puts her hands over Matt's eyes and even kisses him on the cheek. She compels him to help her be more like Elena and to tell her everything he knows about Elena. Later that day, Matt throws a party for Tyler and invites Katherine into the Lockwood Mansion.
In Gone Girl, Katherine tells Matt that she may be the only one who truly sees how beautiful he is. She calls him "the best night she'll never have" suggesting she wanted to engage in a sexual relationship with him. He remains indifferent to her.
- Matt dated her doppelgänger descendant, Elena Gilbert.
- Katherine fooled Matt twice - in The Return and in The Devil Inside - by pretending to be Elena.
- Katherine has admitted that she thinks Matt is hot, often commenting on his blue eyes.
- Katherine and his sister Vicki are the only two characters to call him Matty.
- Katherine has a crush on Matt.
- Matt has slept with Katherine's daughter Nadia.
- Katherine often calls Matt "Matty Blue". She also calls him "Matty Blue Blue" and "Matty Pants".
- Katherine showed a romantic interest in both men Elena gave up on, while never truly having romantic feelings for Damon, who Elena chose. Ironically, the only one of them that actually pursued Katherine was Damon.
- Katherine: "Those blue eyes... they made me soft. I should've ripped your head off when I had the chance.
- - True Lies
- Katherine: "How about now? Matty Blue-Blue. I want another drink."
- Matt: "No! You're drunk and scaring the customers."
- Katherine: "You realize that every single time you say no, it just makes you hotter, right?"
- Katherine: "What are you watching, some Czech reality show?"
- Matt: "How'd you know it was Czech?"
- Katherine: "Eye contact. We're getting started."
- - Dead Man on Campus
- Katherine: (to Matt) "I'm paying you to make me hot again. Whip me into shape and prolong this death thing as long as possible."
- - Fifty Shades of Grayson
- Katherine: "Oh... The one girl here who actually appreciates how beautiful you are. You wouldn't stab me in the heart, would you, Matty Blue? No, I don't think so. You will definitely go down as the best night I never had. Oh, well."
- Matt: "Oh, well."
- - Gone Girl