How Robert Downey Jr.'s Kids Inspired the Most Iconic Line in 'Avengers: 'Endgame' [SPOILERS]

This story includes spoilers for 'Avengers: Endgame.'

Even though the Avengers: Endgame spoiler ban officially ends today, per directors Joe and Anthony Russo, if you have yet to see the movie and don’t want to know the details behind one its most iconic lines, stop reading right now. If you do (and you probably know which line we're talking about), read on.

One of the most memorable lines from the new film is a repeated exchange between Iron Man and his daughter, in which they tell each other “I love you, 3000.” There was not a dry eye in theaters when Tony Stark’s hologram said it back to Morgan Stark after his passing.

And as it turns out, the origins of the line—which has already reached legendary status for Endgame (as well as the Marvel Cinematic Universe as a whole)—has the most wholesome of explanations, as INSIDER reports.

"The line went, 'I love you tons. I love you tons,'" said Endgame screenwriter Stephen McFeely in an interview at 92Y in New York City last week. "And so, [Iron Man] says, 'I love you tons,' but his children [in real life] say to him, 'I love you, 3000.'"

The sweet line has become extremely popular with fans, as many have taken to social media to say “I love you, 3000” to both the late Iron Man and the actor who portrayed him, Robert Downey Jr.

These sentimental moments between Tony and Morgan are even more emotional knowing the real-life backstory.

This article also appears on Mental Floss.