After onetime pop star Paul Anka complained over the weekend that he was the principal composer of "This Is It," the title song of the upcoming Michael Jackson documentary -- and threatened to sue -- the Jackson estate quickly conceded that Anka's claims were justified and quickly granted him 50 percent of the copyright. Just as quickly Anka withdrew his legal challenge, telling the TMZ website, "They realize it's a mistake, they realize it's my song, they realize it's my production of his vocal in my studio and I am getting 50 percent of the whole project, actually, which is fair." Anka claims that he and Jackson worked on the song in 1983 and that the original Jackson recording was intended to "demo" the song for an Anka/Jackson duet album. However, the two performers reportedly had a falling-out and Anka never did record it. (Using the same instrumental track and altered lyrics by Anka, it was released in 1991 with a Latin singer named Sa-Fire providing the vocal.) On the new recording, background vocals are provided by Jackson's brothers. It was posted online by the Jackson estate on Monday, which noted that it was "co-written by the legendary Paul Anka." Meanwhile, the song itself is being slammed by numerous music critics. Jon Parales said in the New York Times that it "won't be on anyone's list of best Michael Jackson songs, even if it's a long list." The Los Angeles Times 's Todd Martens called it "a trifle. ... It does bring the fallen pop icon a little back down to earth."