ThymeTraveller said:
I do mainly portrait photography.
Any specific type, or all? Individuals, groups, etc.? The 24-70mm is a very good general purpose portrait lens, particularly for group shots or in tighter spaces. If you have the space (e.g. outdoors), the 70-200mm f/2.8L IS II is really an excellent portrait lens.
IMO, the 24-70mm is a little too loose for tight shots (head/shoulders), where the 135mm f/2L is excellent. The 85mm f/1.2L is considered by some to be the 'ultimate' portrait lens, but depending on your budget the 85mm f/1.8 delivers excellent IQ and is over a full stop faster than f/2.8 (meaning more OOF blur). For full-body shots, the 50mm f/1.2 is one to consider - it's really designed as a portrait lens, with some undercorrected spherical aberration which produces a superior bokeh (at the expense of some sharpness wide open, but most of the time that's just fine for a portrait).