  The recently discovered colliding-wind binary (CWB) Apep has been shown to
emit luminously from radio to X-rays, with the emission driven by a binary
composed of two Wolf-Rayet (WR) stars of one carbon-sequence (WC8) and one
nitrogen-sequence (WN4-6b). Mid-infrared imaging revealed a giant spiral dust
plume that is reminiscent of a pinwheel nebula but with additional features
that suggest Apep is a unique system. We have conducted observations with the
Australian Long Baseline Array to resolve Apep's radio emission on
milliarcsecond scales, allowing us to relate the geometry of the wind-collision
region to that of the spiral plume. The observed radio emission shows a
bow-shaped structure, confirming its origin as a wind-collision region. The
shape and orientation of this region is consistent with being originated by the
two stars and with being likely dominated by the stronger wind of the WN4-6b
star. This shape allowed us to provide a rough estimation of the opening angle
of $\sim 150^\circ$ assuming ideal conditions. The orientation and opening
angle of the emission also confirms it as the basis for the spiral dust plume.
We also provide estimations for the two stars in the system to milliarcsecond
precision. The observed radio emission, one order of magnitude brighter and
more luminous than any other known non-thermal radio-emitting CWB, confirms it
is produced by an extremely powerful wind collision. Such a powerful
wind-collision region is consistent with Apep being a binary composed of two WR
stars, so far the first unambiguously confirmed system of its kind.
