Which Tolkien work, published in 1998, features a toy dog named Rover?

The Tolkien work published in 1998 that features a toy dog named Rover is Roverandom.

Roverandom began as a children’s story Tolkien told after his son Michael lost a favorite toy dog on a beach in 1925. In the tale, the dog is transformed into a toy and has adventures involving the Moon, the sea, wizards, and the mythical city of Tirion. Tolkien wrote the story for his children but did not publish it during his lifetime.

The book appeared posthumously in 1998, edited by Christopher Tolkien. Its episodic structure and playful tone make it different from Tolkien’s major Middle-earth narratives, although it contains imaginative creatures, invented places, and connections to wider mythology.

Roverandom is sometimes confused with Farmer Giles of Ham or Smith of Wootton Major, which are also shorter Tolkien fantasies. Unlike those works, Roverandom’s starting point is explicitly connected to a real childhood incident involving a lost toy.