Avril Lavigne has called a conspiracy theory that claims she died years ago and was replaced by a lookalike, "weird".

Thought to have originated on a Brazilian fan page dedicated to the Canadian singer, some have speculated that she was replaced by a girl called Melissa earlier this century.

To justify the claim, they suggest that her height, nose and style have altered over the course of her career. This, they claim, is evidence that there have been two different people.

Those who subscribe to the theory believe that Lavigne died in 2003, at some point between the release of her first album Let Go in 2002 and her second record Under My Skin in 2004.

Asked about the persistent rumours in an interview with Australian radio hosts Kyle Sandilands and Jackie O on the KIIS Network, the "Complicated" singer made it clear that she's baffled by the claim.

"Some people think that I'm not the real me, which is so weird," she said. "Why would they even think that?"

In addition to reading into the singer's supposed physical changes, the conspiracy theory delves into her song lyrics as well as alleged clues sprinkled in her albums and songs.

Lavigne has spoken about the conspiracy theory in the past.

Last November she hosted a live stream on Facebook, during which fans were able to ask her questions.

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Someone asked whether the "Sk8ter Boi" singer was dead, to which the singer responded: "No, I'm not dead. I'm here."

"I think it's really silly that anyone would ever believe that," she added. "But yeah, it's this huge rumour."