  We report a failed solar filament eruption that involves external magnetic
reconnection in a quadrupolar magnetic configuration. The evolution exhibits
three kinematic evolution phases: a slow-rise phase, an acceleration phase, and
a deceleration phase. In the early slow rise, extreme-ultraviolet (EUV)
brightenings appear at the expected null point above the filament and are
connected to the outer polarities by the hot loops, indicating the occurrence
of a breakout reconnection. Subsequently, the filament is accelerated outward,
accompanied by the formation of low-lying high-temperature post-flare loops
($>$ 15 MK), complying with the standard flare model. However, after 2--3
minutes, the erupting filament starts to decelerate and is finally confined in
the corona. The important finding is that the confinement is closely related to
an external reconnection as evidenced by the formation of high-lying
large-scale hot loops ($>$ 10 MK) with their brightened footpoints at the outer
polarities, the filament fragmentation and subsequent falling along the newly
formed large-scale loops, as well as a hard X-ray source close to one of the
outer footpoint brightenings. We propose that, even though the initial breakout
reconnection and subsequent flare reconnection commence and accelerate the
filament eruption, the following external reconnection between the erupting
flux rope and overlying field, as driven by the upward filament eruption, makes
the eruption finally failed, as validated by the numerical simulation of a
failed flux rope eruption.
