How to call event from another form in C#

You should study this link Opening form instances in C#

Best Regard,
Theingi Win

this[^] might help you.

The thing is: Load event is not the "real" event in System.Windows.Forms, even thought technically it is the event. Maybe, the idea was to mimic Load event of System.Web.UI for very questionable "compatibility"? Who knows?
Anyway, what happens is this: when form is constructed and the event is fired (if its instance is not null), when InitializeComponent was already called.

For this reason, I never use this event, and do not advise to use it. In my opinion, it is done for marketing purpose, to strengthen the illusion of graphical programming. Instead, have some setup function which I directly call from the form constructor at the very end. I also use a separate file with the partial declaration.

That said, you cannot just fire this event for any reasonable purpose. The event is always fired in the class declaring the event; this is a very event-specific limitation (as opposed to other delegate instances). You can only create a Form instance and show the form and never need anything else related to form "Loading" (which, again is a "fake" notion).

Finally, making extra Form is a common design mistake. Just one Form, with, say tabbing interface is usually enough, but multiple forms are confusing the user. If your really need it, don't forget: make non-main forms owned by the main Form (see Form.OwnedForms) and set Form.ShowInTaskbar to false for non-main forms.

—SA