c# Revert on checkbox unchecked

My goal is when the checkbox is unchecked to have label1 return to it's value before the checkbox was checked.

 private void checkBox1_CheckedChanged(object sender, EventArgs e)
    {
        {
            if
              (checkBox1.Checked)
                label1.Text = textBox1.Text + label1.Text;

            else

                label1.Text = label1.Text; //return to previous value?
        }
    }

The way mentioned above, label1 'sticks' to the value when the checkbox is unchecked.

I tried using the label1.Refresh but it didn't work.

Is there a more effective way to get the result I'm looking for?