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A U.S. judge on Tuesday ruled that Warner/Chappell Music does not own a valid copyright to one of the world's most recognizable songs, "Happy Birthday to You," a decision that brings the song into the public domain.

The highly-anticipated ruling comes in a putative class-action lawsuit filed by several artists against Warner/Chappell, the music publishing arm of Warner Music Group, over the song in 2013 seeking a return of the millions of dollars in fees the company has collected over the years.

Happy Birthday candles displayed on a cake. RuthBlack / Getty Images/iStockphoto

In order to make his ruling, U.S. District Judge George H. King had to delve into the song's long and complicated history, which began in 1893 with the publication of a melody called "Good Morning to All" in a kindergarten songbook, written by a Kentucky woman named Mildred Hill and her sister, Patty.

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That melody eventually came to be sung with the familiar Happy Birthday lyrics, which Patty also claimed to have written, according to court records.

Warner's copyright originated with the Hill sisters' publisher, the Clayton F. Summy Co, later known as Birch Tree and acquired by Warner in 1988. Summy had obtained registrations to "Happy Birthday" in 1935, according to court papers.

"Defendants ask us to find that the Hill sisters eventually gave Summy Co. the rights in the lyrics to exploit and protect, but this assertion has no support in the record," King wrote in his 43-page opinion.

Related: Music Company Does Not Own 'Happy Birthday' Song Copyright, Judge Rules

"The Hill sisters gave Summy Co. the rights to the melody, and the rights to piano arrangements based on the melody, but never any rights to the lyrics," he added.

Warner could not be immediately reached for comment.

"'Happy Birthday' is finally free after 80 years," Randall Newman, an attorney for the artists including filmmakers working on a documentary about the song, told the Los Angeles Times. "Finally, the charade is over. It's unbelievable."

The case garnered attention from around the world not only because the tune is so commonly performed, but because many were not aware it was still under copyright, let alone purportedly owned by a major corporation.

People who sing Happy Birthday in their homes or at private gatherings have typically never been at risk of a lawsuit. But when the song has been used for commercial purposes, such as in films, Warner has enforced its rights, and takes in an estimated $2 million in royalties for such uses each year.