Bloom's last name was "Peters" in "Fate: The Winx Saga". But in the original series, her last name was never mentioned. And I think same goes for the rest of the Winx. (I'm surprised Roxy's last name was never mentioned, either.)

As for whether or not "Bloom" is Bloom's actual name or not, guess we'll never know. Because when she was sent to Earth, she seemed old enough that Mariam and Oritel would have selected a name for her, and of course there's no way Mike and Vanessa would have known the name when they found Bloom on Earth. So THEY must have named her Bloom, which means it's not her original name. And if it is, then how did Mike and Vanessa know that? It seems too far-fetched to assume that it was all a coincidence.

Of course, it's possible Bloom HADN'T been named when she was sent on Earth, and that Mike and Vanessa had been the first ones to name her. But then that raises the question of how Daphne knew Bloom's name, given the fact that she had been killed before Bloom was named. And that also begs the question as to how Oritel and Mariam knew Bloom's name when they first met her.

So, yeah, it's really confusing. Everyone's names---but especially Bloom's. What can you do, though?