Originally the mount of Brand, Loyal apparently departed the field of battle on his master's death and traveled to Shadow Earth in search of his master's daughter. Beatrice was more than happy to see her old friend, alone though he might be, and it was by his offices that she made it most of the way to Amber.
The two remain together; Beatrice tends to treat him as less a mount and more a cherished friend that she just happens to ride.
Loyal is generally polite, even sometimes grave, and perhaps a bit too grown-up for the antics of his friend and former stable-mate, Fiach.