Getting richtextbox to load .txt files and .rtf files

Question

So I'm Currently working on a tabbed notepad using a richtextbox and i've come across a problem.

I want it to be able to open .txt files and .rtf.

The code i'm using to load the file is

 GetRichTextBox().LoadFile(openFile1.FileName);

Meaning it's going to assume it's going to open a .rtf file or something of supported format.

Though if I try to open a .txt file it crashes and tells me my formats not right. 

Though if I use:

 GetRichTextBox().LoadFile(openFile1.FileName, RichTextBoxStreamType.PlainText);

And then try to load up a .rtf file I get something like

"{\rtf1\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fswiss\fcharset0 Arial;}}

{\*\generator Msftedit 5.41.15.1515;}\viewkind4\uc1\pard\f0\fs20 So how the hell\par

Do \par

I fix this\par

Problem\par

}

"

So here is my question.

How can I load both .txt files and .rtf files into my richtextbox

(Heres the full code i'm using)

 
            OpenFileDialog openFile1 = new OpenFileDialog();

           
            openFile1.DefaultExt = "*.rtf";
            openFile1.Filter = "RTF Files|*.rtf|Text Documents|*.txt|All Files|*.*";

           
            if (openFile1.ShowDialog() == System.Windows.Forms.DialogResult.OK &&
               openFile1.FileName.Length > 0)
            {
                

                GetRichTextBox().LoadFile(openFile1.FileName);

Any suggestions?