"Avengers: Endgame" has finally passed the box-office haul of James Cameron's "Avatar," making it the highest-grossing movie worldwide before adjusting for inflation.

On Monday, Cameron shared a fun congratulatory note to Marvel on "becoming the new box-office king." It's a record "Avatar" held for a decade.

The image shows Iron Man floating around in the world of the Na'vi.

The note is part of a tradition going back to the 1970s. The d irectors and friends George Lucas and Steven Spielberg used to take out full-page ads in Variety congratulating each other when one of their films beat the other's at the box office.

Visit INSIDER's homepage for more stories.

Honoring a long-standing tradition, the "Avatar" director James Cameron congratulated Marvel for surpassing his 2009 blockbuster to become the highest-grossing movie worldwide.

After 13 weekends in theaters and a recent rerelease, "Avengers: Endgame" has grossed $2.79 billion worldwide, edging out the gross of "Avatar" as the top earner before adjusting for inflation. Cameron's movie grossed $2.789 billion in theaters.

The official "Avatar" Twitter account shared a poster with a message from Cameron congratulating Marvel on its achievement. It shows Iron Man on the moon of Pandora from the hit movie.

Cameron's poster starts out written in Na'vi. "Oel Ngati Kameie" means "I see you." 20th Century Fox

It says:

"Oel Ngati Kameie, I see you Marvel —

"Congratulations to Avengers Endgame on becoming the new box-office king.

"Jim Cameron"

"Avatar" was the highest-grossing movie for a decade.

"Avengers: Endgame" passed Cameron's 1999 box-office hit, "Titanic," in May as the second-highest-grossing movie (on an unadjusted basis). At the time, Cameron sent a letter of congratulations to Marvel Studios for "sinking" his film.

Cameron's note is part of a tradition dating back to the 1970s between the "Star Wars" director George Lucas and his director pal Steven Spielberg.

It started in 1977, when Spielberg took out a full-page ad in Variety magazine to congratulate Lucas' "Star Wars" on beating "Jaws" at the box office.

The playful ad shows the "Stars Wars" droid R2-D2 catching the shark on the end of a fishing line.

The ad that appeared in Variety for George Lucas. The Academy of Motion Picture Arts and Sciences/Facebook

A few years later, Lucas took out an ad in Variety when Spielberg's "E.T." became the highest-grossing movie in 1982. The ad shows Han Solo and Luke Skywalker lifting E.T. in the air as the rest of the "Star Wars" crew — including Darth Vader — party.

The "Star Wars" characters lifting E.T. Variety

That wasn't the end. When Lucas released the original "Star Wars" trilogy again in theaters in the '90s, Spielberg revived the tradition. After the rerelease beat "E.T.," Spielberg took out another full-page Variety ad.

This time, E.T. gave the box-office crown to R2-D2.

E.T. passing the crown to R2 in a Variety ad. Variety via AP

The ads weren't exclusive to Lucas and Spielberg. When "Titanic" shattered "Star Wars" box-office records, Lucas included Cameron in the fun.

C-3P0 can be seen blaming R2-D2 for the ship sinking. Variety

In recent years, the tradition has included other studios.

Feige sent Universal a congratulatory note when "Jurassic World" broke the box-office record held by 2012's "The Avengers."

The image shows Chris Pratt, who starred in both "Jurassic World" and Marvel's "Guardians of the Galaxy," atop a T. rex holding Thor's mighty hammer. It's cool to see, knowing Spielberg directed the first "Jurassic Park."

Thor was puzzled at how the dinosaur was wielding his mighty hammer. @KevinFeige/Twitter

In 2015, the "Jurassic World" producer Frank Marshall once again passed the box-office torch to Lucasfilm after "The Force Awakens" took the top spot at theaters. This time, the T. rex gave BB-8 a medallion.

The dinosaur gave the box-office medal to BB-8. @LeDoctor/Twitter, Universal

In 2018, after "Avengers: Infinity War" passed "The Force Awakens" with the highest-grossing opening weekend, Lucasfilm's president, Kathleen Kennedy, sent a note to Marvel Studios. (Note that both companies are owned by Disney.)

The note, shared on the official "Star Wars" social accounts, showed Rey handing a lightsaber to Tony Stark's Iron Man to celebrate.

Here's the image the "Star Wars" accounts shared congratulating Marvel's Avengers. Lucasfilm

It says:

"From a Galaxy far, far away... to Earth's Mightiest Heroes, congratulations on the biggest opening weekend in history! "From Kathy and everyone at Lucasfilm!"

In May, "Endgame" passed "Titanic" at the box office. The 1997 Oscar-winning movie was one of the highest-grossing movies for over two decades.

Here's the note of congratulations from Cameron to Marvel and Kevin Feige, the Marvel Studios president, on the achievement. It shows the Avengers logo sinking the ship in the ocean.

The Avengers sank the Titanic in a note from James Cameron to Marvel's Kevin Feige. @JimCameron/Twitter

It says:

"To Kevin and everybody at Marvel, "An iceberg sank the real Titanic. It took the Avengers to sink my Titanic. Everyone here at Lightstorm Entertainment salutes your amazing achievement. You've shown that the movie industry is not only alive and well, it's bigger than ever! "Jim Cameron"

We may have to wait awhile to see another one of these posters. Cameron's been working on his "Avatar" follow-ups for some time. "Avatar 2" is expected to arrive in December 2021.

Read more: Marvel just announced all of its movies for the next 2 years — here they all are