Interactions between surface waves and currents strongly modify the waves characteristics, height and shape, and in favourable conditions cause extreme sea states. In particular current systems, the risk of extreme waves is a known hazard because it is also the place of main shipping routes. It is the case for the Agulhas current where many ships recorded severe damages. Modelling of these interactions in standard wave numerical models is an active area of research, that would benefit from the increased availability and accuracy of satellite observations. Lack of observations of these phenomena has long been a main limitation to their understanding and prediction. We analyse a particular case of a swell system propagating in the Agulhas current by the mean of wind and sea state measurements from several satellites, jointly with state of art analytical and numerical modelling of wave/current interactions. Synthetic Aperture Radar and altimeter measurements are used to show the evolution of the swell train and associated extreme waves. A ray tracing analysis shows that the significant wave height variability at scale under 100 km is associated with the current vorticity patterns. Predictions of the WaveWatch-III numerical model in a version that accounts for wave / current interactions are coherent with observations although their effects are clearly under-predicted in the current configuration. It is shown from altimeter measurements that very large significant wave height gradients are systematically associated with the current patterns, that reflect increased steepness of waves interacting with surface currents.