Ever wonder why birthday celebrations on TV or film are so rarely accompanied by a rendition of "Happy Birthday to You?"

As with many things in life, it comes down to money: doing so is expensive. "Happy Birthday to You," the most popular tune in the English language, is copyrighted. So, using the tune means paying licensing fees.

At least, that used to be the case. On Tuesday, a federal court judge in Los Angeles ruled that copyright on "Happy Birthday to You" is in fact invalid. If the ruling stands, the song will enter the public domain, free for all to use.

That's a blow to Warner/Chappell Music and its parent company, the Warner Music Group, which has held the tune's copyright since 1988 and collects around $2 million in annual licensing fees, according to The New York Times.

Related: 'Smoking Gun' Evidence Could Eradicate Copyright Claims for the World's Most Popular Song

The "Happy Birthday" tune -- which was co-written by Kentucky sisters Patty and Mildred Hill and originally titled "Good Morning to All" -- was first published in 1893 by Clayton Summy, a company later purchased by Warner/Chappell.

The copyright case was filed in 2013 by the independent filmmaker Jennifer Nelson. In July Nelson produced powerful new evidence in the form of a songbook published in 1927 -- eight years before Warner/Chappell's copyrighted version appeared -- that contains the song's lyrics.

Considering that Summy never acquired the rights to the tune's lyrics, the judge ruled, the copyright is invalid.

“Happy Birthday is finally free after 80 years,” Randall Newman, an attorney for the plaintiffs, told The Guardian. “Finally, the charade is over. It’s unbelievable.”

A rousing "Happy Birthday" to us all.

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