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I am afraid that you will not be entitled to inherit under the intestacy rules from your biological father's estate as you have been adopted, and are therefore are classed as a child of your stepfather, and not your natural father.
Your natural father's Estate is therefore divided equally between his adopted children and any other natural children he may have had, who had not been adopted.
I am sorry this is not the answer you were looking for, but it sets out the legal position.