Hidden For a View Model attribute - getting changed property EF

Question

I need to know if 2 attributes have been changed, in order to do some stuff. I think there should be 2 approaches, but I can't figure it out.

I created a ViewModel with an attribute for the old value. In my view:

@{DateTime date =  Convert.ToDateTime(Model.event.fromDate.ToShortDateString());}
@Html.HiddenFor(m => m.previousDate, new { @Value =   date })
@Html.TextBoxFor(model => model.event.fromDate,"{0:dd/MM/yyyy}",new{@class="date"})

In the view Model:

....
public Event event {get; set;}
public DateTime previousDate {get; set;}

And my Event class:

....
DateTime fromDate { get; set; }

When I post the view, the "previousDate" attribute of the ViewModel comes with default time '01/01/1901', and not the one that I set.

I think other approach could be to get changed properties from entity framework, but I haven't been able to do it either.