"Alguien Más" is the fourth single

Single (music)

In music, a single or record single is a type of release, typically a recording of fewer tracks than an LP or a CD. This can be released for sale to the public in a variety of different formats. In most cases, the single is a song that is released separately from an album, but it can still appear...

 from Belinda's second studio album Utopía

Utopía

Utopía is the second studio album by Spanish-born Mexican recording artist Belinda. It was released on October 3, 2006 by EMI Televisa Music in Mexico and Latin America. The album was later released on September 17, 2007 to Europe and the United States...

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Information

The song is about a girl whose boyfriend isn't the same; she feels there is some other girl that he is seeing and she is torn apart and won't forgive him.

Music video

According to the official Belinda's site, the artist filmed the music video in late July 2007. It was to be released but the video was cancelled for unknown reasons.