A surprising twist on Thursday night’s episode of “Grey’s Anatomy” has fans asking: Did that really just happen?

Warning: This post contains a major plot spoiler.

Fans were shocked when the medical drama’s creators killed off one of its main characters in a nail-biting and unexpected twist.

Viewers took to Twitter to vent their frustration, not only with the death of heart-throb Derek “McDreamy” Shepherd, but with the way the show did away with its leading man.

Grey's Anatomy

Shepherd, played by Patrick Dempsey, died from injuries received when he was blindsided in a car crash.

Based on social media, it seems most fans were shocked by the end of episode 21. Here are the main reasons behind fans’ reactions:

1. Deceptive introduction: Viewers know each episode will involve some type of medical crisis. At the beginning of the episode, Shepherd administered first aid to four people injured in a crash, making it seem as though their injuries would be the focus of the show.

Car crash Derek 'McDreamy' Shepherd is dead

2. The crash itself: There are no cars on the road when the four people are rushed to hospital. Suddenly, a transport truck appears out of nowhere and crashes into Shepherd’s car on an otherwise empty roadway.

Derek 'McDreamy' Shepherd is dead Greys

3. Locked-in syndrome: Though McDreamy is gravely injured, viewers were privy to his thoughts in a gut-wrenching inside look at “locked-in” syndrome. Shepherd, a veteran neurosurgeon, is aware of his doctor’s errors and realizes he is doomed, but is unable to speak up because of his injuries.

Grey's Anatomy

4. Wife’s decision: Shepherd’s co-worker and wife Meredith Grey tearfully makes the decision to “pull the plug” on her husband without consulting other doctors or family members.

Grey's Anatomy

5. Song choice: Long-time fans of the show recognized the first notes of “Chasing Cars” by Snow Patrol, the same song that played several seasons ago when another character died. “You know when they play Chasing Cars on Grey’s Anatomy it’s bad,” one fan wrote on Twitter.

"Grey's Anatomy" is available in Canada on CTV and CTV GO.