Pied Heron on the River Taff, Cardiff?

I've spotted a heron like bird on the River Taff in Cardiff this evening. 

Initially thought it was a black heron but it had a colourful face (white/ grey and yellow) and bill (yellow?). Could it have been a pied heron?

I've often seen commorants and grey herons in the same area and am familiar with them (so know this was something different). 

Anyone have any thoughts?