How do I pass data from child of child form to parent form?

Form1:   public partial class Form1 : Form

 {      

  public Form1()     

{         InitializeComponent();       

}      

 private void buttonOpenForm2 _Click(object sender, EventArgs e)     

{         

Form2 frm2 = new Form2();         

frm2.Show();     

}   

}    

Form2:   

public partial class Form2 : Form 

{     

public Form2()     

{         

InitializeComponent();     

}      

 private void buttonOpenForm3 _Click(object sender, EventArgs e)     

{         

Form3 frm3 = new Form3();         

frm3.Show();     

} 

}      

Form3:     

public partial class Form3 : Form   

{     

public Form3()     

{        

 InitializeComponent();     

}      

 private void buttonAddRow _Click(object sender, EventArgs e)     

{         //What to write here to insert the 3 textboxes values into DataGridView?     

 }

 }