A Brazilian blog, Avril Esta Morta (Avril is Dead), speculated several years back about the singer's death, pointing out what it said were inconsistencies in her skin.
A Twitter user who claims to be a 17-year old high school student and has over 13,000 followers detailed the claim in a thread which has since been liked and retweeted almost a quarter-of-a-million times in total, alleging that the singer took her own life in late 2003 after her grandfather's death.
It's the conspiracy theory that keeps coming back around, just like the moon landings and Biggie and Tupac - Avril Lavigne actually died in 2003 and an imposter has taken her place for the last 12 years.
Avril herself has yet to comment on the conspiracy theory.
To make it worth going viral, Dr Rosewarne said a conspiracy theory must have the "right ingredients" - namely some humour, a celebrity and the right setting.
Did you know Avril Lavigne was replaced by a lookalike named Melissa in 2003?
A blogger said: "Launched in 2004, it is completely different to the first CD!"More news: Snap Chat maintained as Hold By Canaccord Genuity
"The "New Avril" poses for photos always sad and morbid expression, sometimes dropped to the ground as if to say something". There was even a publicity shot in which Lavigne had "Melissa" written on her hand.
Others used the hashtag #NotMyAvril, with one accompanying meme saying: "This is a case for the Federal Bureau of Investigation".
She continued to share other background that Twitter users had shared, specifically regarding her change in appearance that just seems off.
The rumours have arisen again thanks to a convinced Twitter user posting a thread of tweets over the weekend.
Since then, though, more and more people have found evidence for the theory, attaining a sort of crowd-sourced legitimacy. The two became friends, and purportedly Vandella was taught to sing and perform like Lavigne.
"The internet has been the flawless medium for the distribution of false information: very quickly a stupid - but often highly entertaining - story can be effortlessly distributed far and wide".