Before “Grey’s Anatomy” aired episode 21, a promo video teased that the installment, titled “How to Save a Life,” would be one that America would never forget -- and boy were they right. The episode kicked off with Amelia (Caterina Scorsone) warning her brother to turn his car around because there was no way he would be able to make his flight to D.C. due to the traffic. But Derek (Patrick Dempsey), being the persistent person he is, decided to take a short cut, one that caused him to witness a brutal car crash.

Derek was shaken up (and rightfully so) after witnessing the two vehicles flip over due to reckless driving. He immediately tried to find his phone to dial for help. But of course it was missing. So, Derek decided that he would have to forgo any calls, which is when he went to work.

First he checked on the car with a mother and daughter. Both passengers were alive. But unfortunately for the second vehicle, the one that caused the crash, both teens were severely injured. Derek noticed the boy who was driving had head damage, an injury that he initially prioritized. However, it was later revealed that the teen girl’s abdomen injury was an even bigger issue.

“You have a little cut in your tummy,” he said to the female car crash victim whose intestines were protruding out of her skin.

“I’m going to die,” she predicted, only to have Derek respond, “Don’t say that. That’s insulting. I don’t let people die.”

With nothing but a teeny, tiny first aid kit Derek put his creative medical skills to work. He used dry cleaning plastic from one of the automobiles to secure the gruesome wound until a smoke signal from the car wreck signaled for help.

Following the arrival of ambulances, viewers began to ease back into their seats -- that is until Derek’s missing phone started buzzing. Derek had begun searching in between his seats for the vibrating device, which is when a truck slammed into his car.

Derek was rushed to the same hospital where the car crash victims were sent. However, due to his head injury, he lost his motor skills and was unable to reveal his identity. Thus Derek getting dubbed “John Doe.” As the surgeons tried to diagnose the mystery patient, Derek began to analyze his own trauma.

“You should have taken me to get a head CT,” he said after the surgeons opt to forgo a brain scan. “ I’m going to die because these people aren’t properly trained.”The untrained surgeons slice Derek open to try to find the source of his bleeding. And after several cuts later they realize that it must be coming from his head. The try to get ahold of the head of neuro but of course the head specialist is at a dinner – and hour and a half away.

“It’s too late. You’re too late,” Derek narrated as the doctors try to save his life.

That’s when episode 21 cuts to the final scene viewers witnessed in the previous installment, the moment where police officers arrived to Meredith’s (Ellen Pompeo) home.

“I’m afraid there’s been an accident. Can you come with us please?” the officials asked her. But what was Mer to do? She had a house full of sleeping children. With her husband’s fate dangling in the air, Derek’s wife dragged her tired babies to the hospital only to learn that her husband was dead.

“Dr. Grey, we can’ tell you how sorry we are for your loss,” a doctor shared his condolences with the new widow. That’s when Meredith grabbed Derek’s charts. She called the doctors out that they made a life-threatening mistake for not getting her husband a CT scan. But that wasn’t the moment that bothered her the most. After just learning her husband was brain dead, a surgeon (the one who decided not to get Derek a CT) began to give Mer “the talk” regarding her husband’s fate: does she keep him on life support of “pull the plug”?

“Give me the papers!” Mer shouted ferociously at the scrub-donning pest.

After singing the papers to end Derek’s lie, Meredith stepped out of the hospital for some air. That’s when one of the doctors (who was assigned Derek’s case) approached her to apologize for what had happened. But instead of Mer freaking out on the doctor for not being “good enough” to save her husband, she advised the surgeon to "be better."

“He was the one that died on your watch. He will haunt you -- the hard ones always do,” she warned, adding that it’s the hard ones that will either make surgeons better doctors or force them to quit (and she doesn’t want Derek’s demise to result in a surgeon quitting). “So get back inside because you’re not saving any lives out here.”

After the doctor rushed back into the hospital, Meredith vomited while coming to terms with her husband’s death. But nothing could prepare Mer for the moment she would have to watch Derek being taken off life support.

“Derek it’s OK. You go," she said with tears streaming down her cheeks (and ours, too!). “I’ll be fine.”

What did you think of episode 21 of "Grey's Anatomy"? Did Derek's death shock you? Sound off in the comments section below.