Each disclosure will be shaped by the circumstances and the people involved. However, there are a few principles of disclosing that can help. Lead with love. Before you say anything else, express your love for the person. Emphasize that whatever else you have to say and that no matter what happens you love that person and will continue to love them.
Love is powerful and Love begets Love.
This expression of love can soften the impact of what you have to say and reduce the intensity of the conflict. If possible, disclose in absentia. What I mean here is to make your disclosure in such a way that you are not present when disclosing. For instance, my therapist suggested sending a letter to my parents. This was great advice.