Hadhrat Ahmad(as) wrote that this revelation relates to the marriage of Hadhrat Ummul Mumineen (ra) (Nuzul-al-Masih, Page 146). This meant that she would be tied in matrimony to the Promised Messiah(as) but then would become a widow.
This is what happened. It had been stated that she would stay alive after his (as) demise. As the prophecy of Muhammadi Begum was related to a lack of repentance, and the subsequent demise of Sultan Mohammad, this revelation fulfilled in the manner mentioned above.
We must remember that a Prophet may isinterpret his prophecies, and we see this even with the Prophet Muhammad (sa). Hadhrat Ahmad (as) orginally did misinterpret this revelation to mean that he would marry a widow, but Allah Corrected him and he publisized this correction.
The revelation was:
“A virgin and a widow”
Hadhrat Ahmad (as) originally stated:
About eighteen years ago, I had an opportunity to visit Maulavi Muhammad Husain Batalavi, Editor of Isha‘atusSunnah at his house. He asked me whether I had received any revelation lately and I mentioned to him the revelation, which I had already mentioned several times to my friends:
I interpreted this to him and to all others to mean that: God has intended to bring two women to me in marriage—the first time a virgin and the second time a widow. The first part of the revelation, relating to a virgin, has been fulfilled. By Allah’s grace, I have four sons from that wife. I await fulfilment of the part about the widow. [Tiryaqul-Qulub, p. 34, Ruhani Khaza’in, vol. 15, p. 201]
This was however a misinterpretation of the Messiah(as), which Allah Corrected. The revelation itself only said “A virgin or a widow” and this prophecy was fulfilled in Hadhrat Nusrat Jahan Begum (ra). Allah Corrected Hadhur (as) and Revealed to him:
تَکْفِیْکَ ھٰذِہِ الْاِمْرَأَۃُ
“This woman will suffice for you”
Meaning, he would not marry again rather Hadhrat Nusrat Jahan Begm (ra) was enough for the Promised Messiah(as). This was revealed during February 16, 1906.