Questions about Jury duty?

Out of curiosity say a person is called for jury duty for a criminal trial and during questioning the juror realizes that the defendant is someone they know like a cousin or brother. But lets say the lawyers and the judge don't know that and the juror pretends to not know the person and is chosen to be a juror for their cousin or brothers court case. What would happen to both the Juror and the defendant if the court DOES find out they are related and the juror lied about this.