On the surface, it seems like Black Beauty wraps up with the happiest of endings. After a traumatic downfall and coming close to death from overwork, Beauty at last finds a home in a beautiful spot with people who will care for him for the rest of his days.
In the last few sentences, he describes the farmer's son who pays him special visits, and the owners who've promised never to sell him. Even better, his groom is Joe Green, who knows Beauty from his younger days at Birtwick Park. "My troubles are all over, and I am at home" (49.22), Beauty says, and we couldn't hope for a sweeter, more satisfying ending for our hero.
But the last line holds a note of something bittersweet, and reminds us of everything Beauty has lost:
[…] often, before I am quite awake, I fancy I am still in the orchard at Birtwick, standing with my old friends under the apple trees. (49.22)
In the happy, secure comfort of his new home, Beauty imagines he's somewhere else. Even now, he's still thinking back to his time at Birtwick with Ginger and Merrylegs, truly the happiest time in his life. It reminds us that Beauty's friend Ginger did not have such a happy ending—and we aren't even sure what happened to Merrylegs. Ending on this note is a poignant reminder that lucky as Beauty is, he's still at the whim of humans, and so are his fellow horses. And many other horses aren't so lucky.