As a fellow man, I can say that just because he's receptive to the toy doesn't mean he'll be okay with the real thing, but I do genuinely thing easing him into it—if you want him to know—will be a better idea, and honestly, if he's a really good partner, like top quality, he'll listen to you without judgement and think about your reasons and come up with his own conclusion, which would be awesome if he said that he was okay with it. But let me repeat again for everyone in the back.
TREAD VERY CAREFULLY
Because if he is not on board, or worse, repulsed by it, he could leave, try and get rid of your other partner, ruin your life, etc.
I don't mean to fear monger you or anything, but I am saying to be careful, as awful people have done worse for less, so trust your own judgement and intuition. Like if you are just having a really bad feeling about telling him but can't explain it, your subconscious is spewing red flags everywhere. Listen to them.
I sincerely hope your partner is receptive to it, as that's many of our hopes for the future is to have a zoo—or at least—zoo tolerate partner. So yeah, good luck, I wish you great happiness!!