Who are Estella’s birth mother and father? How does Pip discover this?

Molly had given birth to Magwitch's daughter, Estella. In chapter 48, Pip has dinner with Jaggers and Wemmick at Jaggers' home and learns from the host that Drummle has indeed married Estella. Jaggers' verdict on the subject is that Drummle, because of his "spidery" character, will either beat her or "cringe," that is, become a brow-beaten husband himself. The whole conversation pains Pip, who has been trying to avoid the subject even with Herbert.

During the dinner, Pip finally realizes what had been so familiar about a certain look he had seen in Estella. It was a look that he had seen in Jaggers' servant woman as well. Pip knows instinctively now that Jaggers' servant woman is Estella's mother!