So, today it happened. I was dreading this conversation and knew that sooner or later the day will come. He called me and said that since we had not seen each other for several months, how about meeting up for a lunch and cup of tea. The moment I saw his number flashing up, I knew that the time has come. A curious look - yeah, he had not seen me for months and those were exactly those months I started the HRT. We had a long conversation about lots of different things and I almost decided that I should better postpone the most important topic for another day, but then... on a second thought... the hell with that. So I steered our conversation back and he looked almost scared - it turned out he thought I might be having a cancer - loss of weight, hints that more of that to be in near future, offering some of my new clothes to him (like I might be dying), a kind of younger face but with something wrong on it - it turned out he noticed that my facial features had changed - but could not figure out how exactly (he agreed that my face had become narrower).
Ugh, so I started with a short lecture on human fetus anatomy, how we all start as girls, the androginisation of brain and that it fails sometimes ---> gender dysphoria (raised eyebrows) ------> transsexualism (something just clicked in his eyes) ----> well, why do You think I am telling You this? -----> because You want to change Your gender? -----> umm, yes... -----> and why the f...k ,You imagined that I wont be wanting You as my friend anymore?
Big sigh of relief on my part

I wanted to hug him, but I thought that it would be over the top.
It turned out, he was informed about TS - he is journalist and writes about a lot of things. He also recently re-read some kind of sci-fi series, which had many TS characters in it - we laughed about this being some sort of sign. He instantly understood that it has nothing to do with sexual orientation, but it turned out that he was not that homophobic either

.
We have been together through many fights and adventures during those years we know each other - including getting each other to hospital at least once, and the police station - when we apprehended one crazy punk who was attacking people on the street.
He also pretty much knew what the HRT means and does, so he said if I will ever have trouble with someone and wont be able to sort that out by myself, then he will come and crack some skulls.
He also said that I have always been "a cool guy" and he hopes I will turn out "a nice girl".
I said that I wont be his hand-to-hand sparring partner anymore, but if he would ever want a swordfighting duel, then I am his girl - as long as I can wield the Scottish broadsword

A huge relief and I have one more ally now

P.S. I also got the first introduction into loosing male privilege, when we went back to my office and he firmly pushed me aside and took my bicycle saying that females should keep away from carrying those heavy things (I know this was mockery and done on purpose, but he had to have his share of fun too... no?

).