Meaning 'Dear Co-Parent'. I can't be the only person with a perfectly amicable but not sexual/romantic relationship with DC's other parent. And am fed up of typing 'DS' dad' and arguing with myself about the apostrophe all the time.
Mind you I have been thinking about whether there might be a better term than co-parent.
Child's Other Parent Who Is Not My Partner? That makes COPWINMPY. No, that won't do. Acronymic cheating could make ChOPWIMP (CHild'sOtherParentWhoIsn'tMyPartner) I suppose. Hmm. So me and Chopwimp took DS to the park...