Chapter 4 indicates that only four people ever knew outside CW and herself: CW's brother, Anne's father and sister Elizabeth and Lady Russell:

"She was assisted, however, by that perfect indifference and apparent unconsciousness, among the only three of her own friends in the secret of the past, which seemed almost to deny any recollection of it. She could do justice to the superiority of Lady Russell's motives in this, over those of her father and Elizabeth; she could honour all the better feelings of her calmness; but the general air of oblivion among them was highly important from whatever it sprung; and in the event of Admiral Croft's really taking Kellynch Hall, she rejoiced anew over the conviction which had always been most grateful to her, of the past being known to those three only among her connexions, by whom no syllable, she believed, would ever be whispered, and in the trust that among his, the brother only with whom he had been residing had received any information of their short-lived engagement. That brother had been long removed from the country, and being a sensible man, and, moreover, a single man at the time, she had a fond dependance on no human creature's having heard of it from him."