What scandal is suggested by Eliza?

Eliza suggests that Mrs. Graham has had a child with a father other than her husband.

“There’s no need to ask my pardon,” replied her friend, “but I see no one here that at all resembles that child, except his mother, and when you hear ill-natured reports, Miss Eliza, I will thank you, that is, I think you will do well, to refrain from repeating them. I presume the person you allude to is Mr. Lawrence; but I think I can assure you that your suspicions, in that respect, are utterly misplaced; and if he has any particular connection with the lady at all (which no one has a right to assert), at least he has (what cannot be said of some others) sufficient sense of propriety to withhold him from acknowledging anything more than a bowing acquaintance in the presence of respectable persons; he was evidently both surprised and annoyed to find her here.”