Rename tab from added form

Question

My problem is that I have inserted a tab to a tabControl and added a Form to it (basically I wanted to display all the forms I was going to open as tabs).

Code for adding form to tabControl as tab in the Main class:

private void new_form_Click(object sender, EventArgs e)
    {
        add = new Add(null);
        add.TopLevel = false;
        add.Visible = true;
        add.FormBorderStyle = FormBorderStyle.None;
        add.Dock = DockStyle.Fill;
        var tabIndex = tabControl1.TabCount;
        tabControl1.TabPages.Insert(tabIndex, "New Tab");
        tabControl1.SelectedIndex = tabIndex - 1;
        tabControl1.TabPages[tabIndex - 1].Controls.Add(add);
    }

When I was using multiple forms it was easy to rename the title from the form class:

    private void surname_Leave(object sender, EventArgs e)
    {
        this.Text = surname.Text;
    }

How can I rename the tab programmatically from inside the added form?

Edit: I know how to rename a tab from the same class. I need to rename the tab from the form I open in the tab.

Answer 1

What I was trying to accomplish I achieved by passing the reference of one to another form.

in Form2:

public Form2()
{
    InitializeComponent();
}

private Form1 mainForm;
public Form2(Form callingForm)
{
    mainForm = callingForm as Form1;
    InitializeComponent();
}

private void surname_Leave(object sender, EventArgs e)
{
    mainForm.setTabTitle = surname.Text;
}

in Form1:

private void new_form_Click(object sender, EventArgs e)
{
    add = new Add(this); \\this part was missing
    add.TopLevel = false;
    add.Visible = true;
    add.FormBorderStyle = FormBorderStyle.None;
    add.Dock = DockStyle.Fill;
    var tabIndex = tabControl1.TabCount;
    tabControl1.TabPages.Insert(tabIndex, "New Tab");
    tabControl1.SelectedIndex = tabIndex - 1;
    tabControl1.TabPages[tabIndex - 1].Controls.Add(add);
}

public string setTabTitle
{
    set { tabControl1.TabPages[tabControl1.SelectedIndex].Text = value; }
}