In this age of spoilers, social media and the Internet in general, it's nearly impossible for a television show to pull off a true stunner.

Clare Crawley falls in love with a suitor immediately on The Bachelorette and leaves the series early, only to be replaced by Tayshia Adams?

Please. That development was known weeks ahead of it playing out on TV.

But Grey's Anatomy pulled off the impossible on Thursday night. 

The ABC drama concluded its Season 17 premiere by having Meredith Grey's found unconscious in the parking lot, seeminly on the verge of death.

Viewers were then taken inside of her mind, where Meredith was imagining herself very much alive, on a beach and mere feet away from...

... her dead husband?!?

Yes.

Patrick Dempsey made a shocking return to the series as Derek Shepherd, four years after his character was written off the program -- presumably because the actor was very much ready to leave.

Not a single outlet leaked word of his return.

No fan had a clue this was happening.

Moreover, this wasn't some random one-off.

Dempsey isn't back for good or anything, but...

"We will see more of [Derek] this season," showrunner Krisa Vernoff told the Los Angeles Times. "This was not just a cameo. He will appear three more times."

How did Grey's Anatomy pull off such a casting coup -- without anyone ruining it ahead of time?!?

Vernoff said Dempsey's appearance was kept "top secret" until the day of filming.

She to the aforementioned newspaper that she even wrote the scene as Meredith envisioning a reunion with her mother Ellis Grey instead of Derek so no one would know.

Not even other writers or cast members.

"We didn't tell the writers for the longest time. When she's walking and she looks as someone is calling to her, and she goes, 'Derek?' In the script, I had it as Ellis Grey," Vernoff said. 

Pretty cool, right?

Added Vernoff:

"And she goes, 'Mom?' We read it at the table that way.

"Nobody knew what we were doing -- to the point that when the crew showed up on the day we shot the scene, nobody knew. It was top secret."

Dempsey himself hhas explained that he and Ellen Pompeo had just started talking again when the actress approached him with the idea of a McDreamy appearance.

"I’ve been tracking what Grey’s had been doing with giving masks, and making sure that people had the right equipment, and it came from that place," the handsome actor told Deadline.

He says that Derek making this sort of return would "make people feel better" and maybe "give [them] some comfort in this time of uncertainty, and that’s how it began."

Dempsey really made it sound like the Covid-19 pandemic, and any small way in which he could help put a smile on the faces of fans, was the main reason he agreed to this.

"It's crazy how much time has passed, but it really was so comforting, and lovely, and inspiring to go back, and to work together, to see everybody," he said.

"It really was so open too.

"That was the thing, really -- people were very, I think, vulnerable in a positive way, where we were all grateful to be there and to be together."

Is there any chance any other character might make a return?

Karev? Yang? Izzie? McSteamy?

Would Vernoff ever bring any of them back?

"I mean, wouldn't it be exciting if we did?" she said to The Los Angeles Times.