- Cecilia: "My God, what an eyesore! Couldn't your father have that hovel cleared away, Tom?"
- Tom Riddle Sr.: "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 Sr.: "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 Sr. 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, Cecilia and Tom Riddle Sr. rode on a grey horse past the house. The two sneered and gossiped at the ruined cottage. 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.
It is possible that Cecilia was Tom's fiancée and intended to marry him soon after the events of this day. If so, it can reasonably be assumed that she was bitterly disappointed and heartbroken when Tom instead appeared to fall for Merope Gaunt, as he was under the influence of her love potion.
Presumably, Cecilia lost contact with the Riddle family after he married Merope. It is unknown what happened to her after Tom abandoned his wife and returned to Little Hangleton in 1926. It is also unknown how she reacted to the deaths of her former paramour and his parents.
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.
- Harry Potter and the Half-Blood Prince (Appears in flashback(s))