  Attempts of Magain et al (2005) to detect the host galaxy of the bright QSO
HE0450--2958 have not been successful. We suggest that the supermassive black
hole powering the QSO was ejected from the observed ULIRG at the same redshift
and at 1.5 arcsec distance. Ejection could have either be caused by recoil due
to gravitational wave emission from a coalescing binary of supermassive black
holes or the gravitational slingshot of three or more supermassive black holes
in the ongoing merger of galaxies which triggered the starburst activity in the
ULIRG. We discuss implications for the possible hierarchical build-up of
supermassive black holes from intermediate and/or stellar mass black holes, and
for the detection of coalescing supermassive binary black holes by LISA.
