And did we mention the fact that Catelyn, in a futile yet courageous bid to save her son, also slit the throat of Walder Frey’s wife? Or that the carnage took place just as young Arya Stark was poised to reunite with her family?

In recent years, high-profile deaths have become increasingly common on prestigious cable dramas like “Mad Men,” “The Walking Dead” and “Boardwalk Empire.” “Game of Thrones” is no stranger to the trend: In Season 1, the ostensible series protagonist Ned Stark was beheaded and his head placed on a spike.

But the death of three major characters (or four, if you count those with four legs) in such spectacularly violent fashion thoroughly shocked fans – or at least those who hadn’t already read the books by George R.R. Martin upon which the series is based.

Sick with despair and vibrating with outrage, many viewers took to – where else? – the Internet Sunday night to express their emotions.

“Tonight's Game of Thrones was the most upsetting hour of TV I've ever seen,” tweeted “Book of Mormon” star Josh Gad.

Other fans were less measured in their reaction. 

PHOTOS: 'Game of Thrones' cast without their costumes

A Twitter account called @RedWeddingTears (warning: link contains profanity) soon began compiling the many angry, invective-and-profanity-laced messages directed at Martin, HBO and the scurrilous Lannister clan; as of Monday afternoon, it had over 9,000 followers and some 250 furious tweets. (“NOBODY WATCH GAME OF THRONES ITS HORRIBLE AND IT WILL MAKE YOUR SOUL CRUSH INTO PIECES AND YOU'LL BE FOREVER CRYING,” read one of the tamer entries.)

For fans of the original books, Sunday was an occasion to gloat, however sympathetically. “Folks watching #gameofthrones who didn't read the books: remember when your really nerdy friend was super sad 13 years ago? This is why!” tweeted one user.

In that spirit, some well-versed fans surreptitiously turned their camera phones on unsuspecting viewers in order to record their horrified responses. By Monday, dozens of “Red Wedding” reaction videos were posted on YouTube.

But even some “Game of Thrones” experts were shocked by the changes made by show runners David Benioff and D.B. Weiss, who altered some of the circumstances of the Red Wedding in order to ramp up the tragedy. In the book “A Storm of Swords,” Robb’s wife is not in attendance at the wedding, nor does Catelyn kill the wife of Walder Frey. (Poor ol’ Grey Wind gets it in the book, though, so you are free to blame that one on Martin.)

In an interview with Hero Complex, Benioff explained the decision-making process. “If there’s ever a fork in the road, and we have to choose between absolute fealty to the novels or what we think is best for the series, we’re always going to take the second turn and stick with the series.”

Still others criticized “Game of Thrones” for amplifying what was already a hearthbreaking event with needlessly gratuitous violence – i.e. repeatedly stabbing pregnant Talisa in the stomach. Calling the episode “offensive and appalling,” Mediaite columnist Joe Concha declared on Monday that, yes, he was going to cancel his HBO subscription.

For his part, Martin understands the emotional outpouring.

“I try to make the readers feel they’ve lived the events of the book. Just as you grieve if a friend is killed, you should grieve if a fictional character is killed,” he said in an interview with EW.

Mission accomplished.