DJ and drummer Joshua McKenzie - known as his stage name MckNasty - is the older brother of Labrinth, an act signed to Simon Cowell's Syco record label.
[Left: Labrinth / Right: Joshua McKenzie]
MckNasty has performed at festivals such as Glastonbury and has toured with acts including Tinie Tempah and Lady GaGa.
However, fans at the audition spoke of their surprise when Cowell appeared to already know the 27-year-old, The Sun reports.
An insider said: "It looked like someone had been pulling strings. Simon went to ask Joshua a question - he said, 'Do you have any... tell me something interesting about you'.
"It was as though Simon was going to ask if he had any famous relatives, that he already knew who he was."
McKenzie said that he hoped to be recognised for his own talent rather than his famous sibling.
He said: "I'm always at the back and I want to be at the front. My brother is Labrinth, he is pretty cool. I like the fact that I have to chase him."
A Britain's Got Talent spokesman said: "To claim that he has been given any advantage is ridiculous and totally untrue. He wowed the audience and went through on his own merits."
Labrinth became the first non-talent show act to sign to Cowell's Syco label in six years back in 2010.
Simon Cowell and David Walliams are said to have clashed at the Britain's Got Talent auditions this week after making several jibes at each other.
Watch Simon Cowell and Ant & Dec talk to Digital Spy below: