B_z magnetogram of NOAA AR 11726 on 22 April, 2013 08:36 UT taken from the processed and re-projected SDO/HMI vector magnetogram series (Sect. 3.2) Please avoid the use of the slashes. For details, refer to Sect. 2.9 of the language guide. Please check for this throughout. The central structures related to the activity discussed in this paper have been pinpointed. The vertical white dashed line shows the photospheric cut of the x = 76 Mm plane used to find and track a pre-eruptive flux rope system in our data-driven simulation (Sect. 4). An animated version of the figure can be found online.