It has been reported the missing toddler is the nephew of Five Second of Summer’s guitarist, Michael Clifford.
Clifford, 21 and William's biological father Brendan are believed to share the same father, Daryl Clifford.
According to The Daily Mail, William's grandmother Natalie Collins revealed the that she was in a relationship with Daryl in the 1980s.
The news comes to light after the court allowed information of William’s time in foster care to be published at the time of his disappearance.
William has now been missing for almost three years.