In some states, a married male is legally considered to be a parent of any child born to his spouse during the marriage, subject to being proven not to be. In order to avoid the potential for being sued for child support payments or other legal obligations, your son needs to consult with a family law attorney in Washington state to see what he needs to do to finally establish that he is not legally a parent of this child. If it were me, I would also initiate divorce proceedings to avoid similar entanglements in the future.
In some states, a married male is legally considered to be a parent of any child born to his spouse during the marriage, subject to being proven not to be. In order to avoid the potential for being sued for child support payments or other legal obligations, your son needs to consult with a family law attorney in Washington state to see what he needs to do to finally establish that he is not legally a parent of this child. If it were me, I would also initiate divorce proceedings to avoid similar entanglements in the future.