The Mark of Cain by Carolyn Wells

When, in his conversation with Judge Hoyt, Terence McGuire stated that his wardrobe purchases were made under the guidance and jurisdiction of his sister, he was creating a fabrication of purest ray serene. For, in this sorry scheme of things, no sister had been allotted to Fibsy, nor, until that moment, had he ever felt need of one. So, the need arising, a sister easily sprang, full fledged, from the red head of the well-named inventor.

Fibsy, likewise was unprovided with parents, and lived with a doting aunt. This relative, a knobby-coiffured spinster, was of the firmly grounded opinion that the orb of day has its rising and setting in her prodigy of a nephew. That he was not a bigoted stickler for the truth, bothered her not at all, for Fibsy never told his aunt lies, at least none that could possibly matter to her.