Simpson, who used to play in British group Busted, has a double who has turned up at a number of Fightstar gigs.
And even his own family have mixed up the bushy-browed twosome.
Simpson says, "This guy is doing my head in. What if my girlfriend runs off with him?"
A source adds, "Charlie is genuinely a little freaked out by this lad. He's the absolutely spitting image of him and keeps appearing at all Charlie's shows.
"He dresses up exactly like Charlie and even had his photo taken with him the other day after a gig.
"It's a surreal sight when the two are side by side."