How did the Prophet marry his adopted son's wife, Zaynab bint Jahsh?

Allah Almighty narrated in the Holy Quran the story of the marriage of the Prophet, peace and blessings be upon him, to Zaynab bint Jahsh, when He said to Zayd ibn Harithah, may Allah be pleased with him: "Keep your wife and fear Allah," even though He knew that Zayd would divorce her and that he (the Prophet) would marry her. The Prophet, peace and blessings be upon him, concealed this matter within himself, fearing people's talk, but Allah made it manifest. After Zayd divorced Zaynab by his own choice, Allah married her to His Prophet, in order to remove any difficulty for the believers in marrying the divorced wives of their adopted sons.