Hi, you can achieve it in RowDataBound event of gridview.
protected void YourGrid_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
Label lbl = (Label)e.Row.FindControl("LabelID");
string[] value = lbl.Text.Split('/');
if(value.Length > 0)
{
lbl.Text = value[0];
}
lbl.ToolTip = your value;
}
}
Hope it helps you.
Thanks.