"He is my future husband."
Translation:Αυτός είναι ο μελλοντικός μου άντρας.
Because when something doesn't sound as natural, it's best to be avoided.:P
There are probably more than a few ways to rephrase a sentence in Greek, and grammatically, all of them could be correct. However, we are not trying to teach every sentence structure that exists, let alone the most uncommon ones. Sometimes they sound fine, sometimes they just sound awkward. In other words, one could use some of them and get away with it in some cases (unfortunately, these cases are not something that can easily be explained. It's just a matter of what sounds best), but if they're talking or writing to a native speaker, uncommon structure is one of those things that will point out the fact that they're not a native. Sometimes, it's better to compromise with the best translation, than searching for ways to rephrase it, risking awkwardness in speech. :P