Warning: This article contains SPOILERS for Avengers: Endgame.

Iron Man, had played the character in 10 films, and each time, he brings his A-game, But his latest outing as the genius billionaire might just be his best.

Capping of Stark's long stint as a superhero in a poetic way, MCU's inaugural hero died a hero when he sacrificed his life in order to take down Thanos and ensure the future of the universe. But before his emotional demise that even included an Avengers: Infinity War. The father and daughter have a couple of adorable moments in the movie, but one that stuck to fans is their final exchange. While tucking Morgan to sleep, Stark tells her, "I love you tons," to which his daughter replies, "I love you 3000."

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When asked about the origin of the line during a conversation at the 92Y hosted by New York Times' reporter Dave Itzkoff which Business Insider attended, Markus and McFeely shared how that exchange came to be. Apparently, the script originally went "I love you tons. I love you tons." However, Downey, who actually tell his real-life kids "I love you tons" shared that his children reply with "I love you 3000" which they adopted. The actor has three kids, and it wasn't clear which one of them he has this exchange, nevertheless, it's obviously an important line to him that's now immortalized in Endgame.

Robert Downey Jr as Tony Stark and Gwyneth Paltrow as Pepper Potts in Avengers Infinity War

This is not the first time that an iconic line from an MCU film had a fascinating origin. came from a Make-A-Wish kid visitor on the set who suggested the piece of dialog. Director Taika Waititi and the actor moved forward with it as it actually makes sense given the situation between the co-Avengers.

As for the "I love you 3000" line, the phrase is now used online by fans of the MCU who express their love for the franchise, particularly for Downey and Stark. Avengers: Endgame wrapped up the arc of the universe's inaugural hero in such a satisfying way. And while it's bittersweet seeing him die, it's the best send off  for the character as it's in the service of everything that he's been through in the last decade. The fact that the dialog has personal meaning to Downey is perhaps one of the reason why the execution of Tony's back-and-forth with Morgan resonated this much to fans.

More: Avengers: Endgame's Post-Credits Surprise Explained

Source: Business Insider