  The TESS mission has enabled discoveries of the brightest transiting planet
systems around young stars. These systems are the benchmarks for testing
theories of planetary evolution. We report the discovery of a mini-Neptune
transiting a bright star in the AB Doradus moving group. HIP 94235 (TOI-4399,
TIC 464646604) is a Vmag=8.31 G-dwarf hosting a 3.00 -0.28/+0.32 Rearth
mini-Neptune in a 7.7 day period orbit. HIP 94235 is part of the AB Doradus
moving group, one of the youngest and closest associations. Due to its youth,
the host star exhibits significant photometric spot modulation, lithium
absorption, and X-ray emission. Three 0.06% transits were observed during
Sector-27 of the TESS Extended Mission, though these transit signals are
dwarfed by the 2% peak-to-peak photometric variability exhibited by the host
star. Follow-up observations with CHEOPS confirmed the transit signal and
prevented the erosion of the transit ephemeris. HIP 94235 is part of a 50 AU
G-M binary system. We make use of diffraction limited observations spanning 11
years, and astrometric accelerations from Hipparchos and Gaia, to constrain the
orbit of HIP 94235 B. HIP 94235 is one of the tightest stellar binaries to host
an inner planet. As part of a growing sample of bright, young planet systems,
HIP 94235 b is ideal for follow-up transit observations, such as those that
investigate the evaporative processes driven by high-energy radiation that may
sculpt the valleys and deserts in the Neptune population.
