- Cecilia: "My God, what an eyesore! Couldn't your father have that hovel cleared away, Tom?"
- Tom Riddle Snr: "It's not ours. Everything on the other side of the valley belongs to us, but that cottage belongs to an old tramp called Gaunt, and his children. The son's quite mad, you should hear some of the stories they tell in the village..."
- Cecilia: "Tom, I might be wrong--but has somebody nailed a snake to that door?"
- Tom Riddle Snr: "Good lord, you're right! That'll be the son, I told you he's not right in the head. Don't look at it, Cecilia, darling."
- — Cecilia and Tom Riddle Snr riding in Little Hangleton[src]
When Bob Ogden, in the course of his duties as Head of the Magical Law Enforcement Squad, visited the Gaunt shack in Little Hangleton to interview Morfin Gaunt about hexing a local Muggle (her boyfriend), Cecilia and Tom rode on a grey horse past the house. The two gossiped at the ruined cottage, Cecilia asking Tom to tear down the hovel who explained an old tramp was the owner of the cottage and thus he couldn't tear it down. The two then talked about Marvolo's son, Morfin, who was believed to be insane by the town. The two were disgusted and horrified to see Morfin had nailed his snake to the door. Later, when Ogden ran from the house to escape Morfin Gaunt's hexes, he knocked into Tom and Cecilia's horse, making the couple laugh at him for his bumbling and silly clothing.
Presumably, Cecilia lost contact with the Riddle family after Tom married Merope. It is unknown what happened to her after Tom abandoned his wife and returned to Little Hangleton in 1926, although it may have been possible that had she not married that Tom may have resumed his relationship with Cecilia. It is also unknown how she reacted to the deaths of her former paramour and his parents.
It is unknown whether she has died.
While Cecilia had very little screen time, she seemed to be snobbish and rude, moreso then Tom Riddle. As she was less polite when talking about the Gaunt family house. Tom Riddle was affectionate with her, calling her darling, and comforting her when seeing Morfin's dead snake nailed to the door.
The name "Cecilia" is the Latinate feminine form of the Roman family name Caecilius, which was derived from Latin caecus "blind". Saint Cecilia was a semi-legendary 2nd- or 3rd-century martyr who was sentenced to die because she refused to worship the Roman gods. After attempts to suffocate her failed, she was beheaded. She was later regarded as the patron saint of music and musicians. The name may also be close to "cecaelia", a Greek mythological creature with the upper torso of a human and the bottom torso of an octopus.
- Harry Potter and the Half-Blood Prince (Appears in flashback(s))