  Coronal mass ejections (CMEs) are the most spectacular eruptive phenomena in
the solar atmosphere. It is generally accepted that CMEs are results of
eruptions of magnetic flux ropes (MFRs). However, a heated debate is on whether
MFRs pre-exist before the eruptions or they are formed during the eruptions.
Several coronal signatures, \textit{e.g.}, filaments, coronal cavities, sigmoid
structures and hot channels (or hot blobs), are proposed as MFRs and observed
before the eruption, which support the pre-existing MFR scenario. There is
almost no reported observation about MFR formation during the eruption. In this
letter, we present an intriguing observation of a solar eruptive event occurred
on 2013 November 21 with the Atmospheric Imaging Assembly on board the
\textit{Solar Dynamic Observatory}, which shows a detailed formation process of
the MFR during the eruption. The process started with the expansion of a
low-lying coronal arcade, possibly caused by the flare magnetic reconnection
underneath. The newly-formed ascending loops from below further pushed the
arcade upward, stretching the surrounding magnetic field. The arcade and
stretched magnetic field lines then curved-in just below the arcade vertex,
forming an X-point. The field lines near the X-point continued to approach each
other and a second magnetic reconnection was induced. It is this high-lying
magnetic reconnection that led to the formation and eruption of a hot blob
($\sim$ 10 MK), presumably a MFR, producing a CME. We suggest that two
spatially-separated magnetic reconnections occurred in this event, responsible
for producing the flare and the hot blob (CME), respectively.
