Think back to when you were told yourself– or how you would like to have been told. This should help you think about the best way to say what you want to say. Practice what you will say ahead of the conversation and keep it simple and clear. You can always say more later. Be prepared for their response as they may feel fear, anger or confusion. They may say ‘why didn’t you tell me before’.
Think about what you would say to each question they might have. Also think about the different ways they might react and how this could make you feel.
Also, work out how you will keep calm if they get emotional or angry and who you can turn to for support if it doesn't go as well as you hoped. Most people have a good response to telling someone but it is always good to be prepared, and remember, even if someone reacts badly, they probably just need a bit of time to think it all through.