Soon to be ex-husband or should I say wife?

Long story short my ex-husband and I separated in October 2016. It was very nasty at first, but we have come to terms with everything and are better than ever just as friends. I always knew he was different. He came out to me that he was gay. He has felt this way since high school and was trying to hide his homosexuality. I support him and his decisions. As time is going by he told me yesterday that now he is looking into becoming a woman. There is nothing wrong him wanting to be a female, but how am I suppose to react to that. We were married for almost 5 years and all of a sudden he wants to be a woman. I would greatly appreciate any kind of advice! Thanks in advance💙 😘