His house was not far off; and as the street-door opened into the sitting-room, and he bolted in with a precipitation quite his own, we found ourselves at once in the bosom of the family. Mr. Micawber exclaiming, “Emma! my life!” rushed into Mrs. Micawber’s arms. Mrs. Micawber shrieked, and folded Mr. Micawber in her embrace. Miss Micawber, nursing the unconscious stranger of Mrs. Micawber’s last letter to me, was sensibly affected. The stranger leaped. The twins testified their joy by several inconvenient but innocent demonstrations. Master Micawber, whose disposition appeared to have been soured by early disappointment, and whose aspect had become morose, yielded to his better feelings, and blubbered.

Hi All, I am confused about who the stranger is in "nursing the unconscious stranger of Mrs. Micawber’s last letter to me". Could you explain this to me. Thanks!

From chapter 52 of David Copperfield by Charles Dickens:

His house was not far off; and as the street-door opened into the sitting-room, and he bolted in with a precipitation quite his own, we found ourselves at once in the bosom of the family. Mr. Micawber exclaiming, “Emma! my life!” rushed into Mrs. Micawber’s arms. Mrs. Micawber shrieked, and folded Mr. Micawber in her embrace. Miss Micawber, nursing the unconscious stranger of Mrs. Micawber’s last letter to me, was sensibly affected. The stranger leaped. The twins testified their joy by several inconvenient but innocent demonstrations. Master Micawber, whose disposition appeared to have been soured by early disappointment, and whose aspect had become morose, yielded to his better feelings, and blubbered.

I am confused about who the stranger is in "nursing the unconscious stranger of Mrs. Micawber’s last letter to me". Could you explain this to me?