“AND THUS endeth our warm, fuzzy holiday lesson: Never take those you love for granted, for they can be gone in a flash.”

So wrote one of the would-be passengers on one of the doomed 9/11 flights — a man who is only with us today because he was late for his plane.

Such is the less-wisecracking side of “Family Guy” creator Seth MacFarlane, who tweeted those words last night. And such is MacFarlane’s momentarily sober-minded nod to the fickle fate of time.

And thus endeth our warm, fuzzy holiday lesson: Never take those you love for granted, for they can be gone in a flash.

— Seth MacFarlane (@SethMacFarlane) December 16, 2013

Naturally, the animator soon undercut that sentiment with a joke about whether his Fox show would really permanently kill a primary character, tweeting in part: “We’d have to be f-----g high.”

“Family Guy.” (FOX via AP)

On Sunday night, through the magic of time-travel, MacFarlane indeed [spoiler alert] reversed the mortal fate of “Family Guy” canine Brian Griffin, who in November was seemingly killed by a careening car.

In the latest episode, baby genius Stewie saves the literate, cocktail-loving dog from the car-wreck death through a twist of time-travel. (There’s that theme of twists of time determining life and death again.)

Brian’s reply: “Wow, Stewie, thank you for saving my life.” Brian then jokes that many other families would have just gotten a new pooch -- which the Griffins actually had done. (The new canine was voiced by “The Sopranos’ “ Tony Sirico.)

After the show “killed” Brian in a mid-November episode, fans on social media let out their disbelief and dissatisfaction — and a Change.org petition demanding Brian’s return gained more than 125,000 supporters.

Of course, “Family Guy,” like many animated shows, is in production nearly a year in advance. Besides, future plot synopses for the series mentioned Brian, so hope appeared on the horizon.

In Sunday’s episode, time-traveling Stewie even says: “Merry Christmas, Brian.”

This is one holiday return that fans can appreciate. Even MacFarlane seemed to be in a giving mood, tweeting Sunday after the ratings-friendly stunt:

“Oh and hey... thanks for caring so much about the canine Griffin. He is overcome with gratitude.”