12 months ago he was causing all kinds of murder and a few of the reds i know wanted him out. I think 50m for him in the time span of January - April last year seems about reasonable, all things considered.
No doubting his ability, he is a top player and is scoring goals for fun at the moment. So in your opinion he is suddenly worth around 90m just from playing 15 games this season (off the top of my head).
Has been brilliant since the start of last season....honestly at the current ever increasing market price for top players, that's not unreasonable to except at all