We plot the Secular Light Curves (SLCs) of comets C/2011 L4 Panstarrs and C/2012 S1 ISON.The brightness of C/2011 L4 Panstarrs and C/2012 S1 ISON increase steeply after discovery but both decrease in slope sharply at ~4-5 AU, a characteristic of Oort Cloud cometary light curves that we refer to as a Slope Discontinuity Event (SDE).After the SDE, the SLC of C/2011 L4 continues to increase and has a surge near perihelion.The SLC of comet C/2012 S1 ISON on the other hand, is very odd and exhibits a SDE plus a near-standstill after the event.We found five comets with similar behavior: C/1996 Q1 Tabur, C/1999 S4 LINEAR, C/2002 O4 Hönig, C/2010 X1 Elenin and C/2012 T5 Bressi, all of which disintegrated.Thus we predict that comet ISON will disintegrate too.We compiled published production rates of water, dust and CO and used them to calculate the Mass Loss Budget.We use this information for ISON to calculate the diameter and to plot 29 comets in an Evolutionary Diagram that separates comets by class.We find a diameter D = 1030±70 m in excellent agreement with the upper limit found by Delamere et al. (2013), D(mean) < 1126 m.It is evident that the Secular Light Curves, exhibit complexity beyond current scientific understanding.Note: The comet disintegrated as predicted (CBET 3731), while this paper was being refereed.