We know that any aircraft will stall at it´s stall speed (for an specific weight, CG position, etc.) but also, that the same airplane will always stall at the same angle of attack.
I´ve read that IAS is just the easy way to control AOA, because in reality it´s all about AOA and nothing to do with airspeed. That when changing IAS we are changing the relative wind and thence AOA.
In the other hand, I know that the critical AOA doesn´t change with weight, (it will always be the same for a given airfoil), but the stall speed will.
There are also high speed stalls... 
Im confused. Can we get into a stall without reaching the critical AOA? What´s exactly the relationship between AOA and IAS?
Thank you