In C# I need to open an mdichild form from another form other than the mdiprincipal itself, but I cannot configure the mdiparent

Question

private void button1_Click(object sender, EventArgs e) {

 FrmUsuario frmUsuario = new FrmUsuario
 {

     MdiParent = principal
 };
 frmUsuario.Show();
 bool a = frmUsuario.IsMdiChild;
 MessageBox.Show(a.ToString());

} The form object is open from other secondary form, although don't not open like mdichid, only opens normally. how do make open this form in secondary form like mdiparent of mdiprincipal.obs: this form frmUsuario opens normally like mdichild in mdiprincipal.

Open the form frmusuario in frmbuscarusuario like mdiparent.