  In this paper we use neutral hydrogen HI and optical spectroscopic
observations to compare the timescales of a merger event, starburst episode and
radio-AGN activity in the radio galaxy B2 0648+27. We detect a large ring-like
structure of HI in emission around the early-type host galaxy of B2 0648+27
(M_HI = 8.5 x 10^9 Msun, diameter = 190 kpc). We interpret this as the result
of a major merger that occurred > 1.5 Gyr ago. From modelling optical long-slit
spectra we find that a young stellar population of 0.3 Gyr, indicative of a
past starburst event, dominates the stellar light throughout the galaxy. The
off-set in time between the merger event and the starburst activity in B2
0648+27 suggests that the starburst was triggered in an advanced stage of the
merger, which can be explained if the gas-rich progenitor galaxies contained a
bulge. Although the exact age of the radio source remains uncertain, there
appears to be a significant time-delay between the merger/starburst event and
the current episode of radio-AGN activity. We also observe an outflow of
emission-line gas in this system, which is likely related to superwinds driven
by the stars that formed during the starburst event. We argue that the radio
galaxy B2 0648+27 is a link in the evolutionary sequence between Ultra-Luminous
Infrared Galaxies (ULIRGs) and genuine early-type galaxies.
