  Switchbacks are sudden, large radial deflections of the solar wind magnetic
field, widely revealed in interplanetary space by the Parker Solar Probe. The
switchbacks' formation mechanism and sources are still unresolved, although
candidate mechanisms include Alfv\'enic turbulence, shear-driven
Kelvin-Helmholtz instabilities, interchange reconnection, and geometrical
effects related to the Parker spiral. This Letter presents observations from
the Metis coronagraph onboard Solar Orbiter of a single large propagating
S-shaped vortex, interpreted as first evidence of a switchback in the solar
corona. It originated above an active region with the related loop system
bounded by open-field regions to the East and West. Observations, modeling, and
theory provide strong arguments in favor of the interchange reconnection origin
of switchbacks. Metis measurements suggest that the initiation of the
switchback may also be an indicator of the origin of slow solar wind.
