Grey's Anatomy fans were thrown for a loop on Thursday when the show said goodbye to Alex Karev (Justin Chambers) by sending him off to go live with his ex-wife, Izzie (Katherine Heigl), and their two kids that he didn't know they had.

For OG Grey's fans, Izzie's impact on Alex is something embedded in our memory, but for those who have recently climbed aboard the Grey's train and aren't completely familiar with the dysfunctional couple's history, this article is for you. Though, since it's been over 10 seasons since we've seen the two together, it also works as a refresher for Grey's Anatomy fans who don't remember exactly what went down between the two surgeons before Izzie left for good in Season 6. So, let's get in our time machine and break down exactly what happened between Alex and Izzie, and maybe it'll help explain why he would be so drawn to this idyllic life in Kansas.

The Beginning

Alex and Izzie started as interns together at Grey Sloan (known back then as Seattle Grace), along with Meredith (Ellen Pompeo), Cristina (Sandra Oh), and George (T.R. Knight). They had a contentious relationship at first, especially after Alex distributed erotic modeling photos of Izzie that she had posed for in order to pay for med school. However, they eventually became close friends, which the other interns gave her crap for.

They tried dating in the early seasons, but Alex screwed it up when he cheated on Izzie with a nurse. That caused a lot of friction between the two and their friend group. However, they managed to get back to a platonic level when Alex needed help studying for his second round of the board exams. They even started sleeping together until Denny Duquette (Jeffrey Dean Morgan) returned to the hospital and Izzie officially blew Alex off and fell in love with Denny instead.

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The Brain Tumor

Izzie spent a long time mourning Denny after his death (explaining that would require a whole other post), but the sparks began to fly for her and Alex again in Season 5. However, at the same time, Izzie developed an incredibly terrifying brain tumor. Alex stuck by her side, despite the fact she was having visions of Denny that she got intimately familiar with, and pushed her to get the help she needed to survive.

To distract herself from the cancer treatments and the possibility of dying, Izzie focused on planning Meredith and Derek's (Patrick Dempsey) wedding. When the magical day came, Meredith and Derek wrote their vows on a Post-it note and gave the dream wedding to Alex and Izzie instead. Izzie made it down the aisle with the help of George and the two married in front of their family and friends. Two episodes later, Izzie had the surgery that saved her life.

Justin Chambers and Katherine Heigl, <em>Grey's Anatomy</em>Justin Chambers and Katherine Heigl, Grey's Anatomy

The Exit

Izzie was fired from Seattle Grace after accidentally giving a patient the wrong dosage of a medicine, which caused the patient to miss out on a much-needed kidney transplant. Even though Alex was partly responsible for the mix-up, Izzie ended up on the hook for it. She was so angry that she just wrote him a letter and left (the irony of this form of breakup is not lost on us, Grey's fans).

That was essentially the end of their relationship. Though Izzie did return later in Season 6 to try and rekindle things with Alex, he realized he deserved better than to be jerked around. He turned her down and Izzie was never to be seen or heard from again. That is, until now.

Kansas

According to Alex's letters to Meredith, Bailey (Chandra Wilson), and Jo (Camilla Luddington), he got back in contact with Izzie around the time of Meredith's medical board trial. He was going to ask her for a testimony to help Meredith keep her job, but the conversation led to the revelation that Izzie had used hers and Alex's frozen embryos they had saved when she had cancer, and they had twins — Eli and Alexis. Upon hearing that he had two children, Alex snuck away to see this family that he never knew he had and immediately fell back in love with Izzie.

Afraid that he wouldn't be able to return to Kansas if he had to face the people he was hurting in Seattle, Alex wrote the closest people in his life a letter to explain why he had left them. Izzie was Alex's first true love, and the first person to truly push him to be a better man. Jo deserves better than a breakup letter, but the fact that Alex ended up with Izzie feels in line with the early seasons of the show.

Grey's Anatomy airs Thursdays at 9/8c on ABC.