Fabulous is a female Burmese she-cat that appears in Das Duel. She's described as a beautiful cat, and Francis has already had his eye on her from some time, hoping to court and mate with her in spring. However Francis is surprised to see the she-cat in company of Adrian and two other females. The detective is disappointed of this and make mistakes in front of the other cats, while analyzing the body of a murdered cat. Despite the outcome of the meeting, Fabulous reveals to Francis that she actually saw the same mysterious shadow that Francis glimpsed.
(SPOILER) It's later revealed that Fabulous's interest for Adrian was nothing of instinct-driven. She was actually investigating and keeping an eye on the events, because she's linked with the mysterious AnimalFarm group. In the ending of the novel, it's revealed how she's the biological mother of the hybrid creature Max, and still craved to protect him.
As the result of the dramatic fire ignited by Max himself (to destroy his creator and the laboratory), Fabulous walked straight into the fire to rejoin her son in death.