Momsen penned Montag`s song at age of eight

London: Taylor Momsen said that she penned down Heidi Montag`s debut hit single when she was just eight years old.

The actress-and-rocker insisted that she was thrilled to hear the song `Blackout` but didn`t have the heart to tell the reality TV star the history of the tune, Contactmusic reported.

"I recorded it with a producer as a demo. Heidi Montag just recently sang it and put it out as her single. I`m like, `OK, dude, you`re singing an eight year old`s words, but that`s cool`. It`s so funny, because I didn`t shop it or anything and I get this call going, `Did you write a song for Heidi Montag?` And I`m like, `What?`," said the 17-year-old star.