Have you ever heard someone refer to a relative as their “own flesh and blood”? This is an expression often used today (usually in a dramatic sort of way, e.g., “But he’s your own flesh and blood!!!”).
Shakespeare used this expression often in his plays (such as Hamlet and Merchant of Venice).
Some argue that Shakespeare took this saying from the Bible (which would have been a familiar text for his audience members). The words “own flesh and blood” also appear, for example, in the New Testament.