  We report the discovery of unusually strong optical and X-ray emission
associated with a knot in the radio jet of PKS B1421-490. The knot is the
brightest feature observed beyond the radio band, with knot/core flux ratios
\~300 and 3.7 at optical and X-ray frequencies. We interpret the extreme
optical output of the knot as synchrotron emission. The nature of the X-ray
emission is unclear. We consider a second synchrotron component, inverse
Compton emission from a relativistic, decelerating jet, and the possibility
that this feature is a chance superposition of an unusual BL Lac object.
