How to find where form was called from

Hi,

I have 3 forms, form1, form2, form3

form 3 can be called from forms 1 and 2 but it loads different information depending on the form it was called from.
I need to do something like this

in the form load function of form 3

if loaded from form 1
'do something
else
if loaded from form 2
'do something else.

Would really appreciate any help with this!

Thanks!