Method returns bool but needs to call another method asynchronously first to determine what should be returned

I have a method called in a Windows form called "Save". It returns a boolean (True if saving was successful, False if it was not). Within this method, I'd like to asynchronously call a web method which performs the actual saving of my data. However, I don't know how return the boolean value from the Save() method AFTER the asynchronous operation is completed.

Simplified, my code currently looks like this:

//Button click event handler for the Save button
private void btnSave_Click(object sender, EventArgs e)
{
       //Close the form ONLY if the Save operation was successful
       if (Save() == true)
       {
            this.Close();
       }
}

private bool Save()
{
      MyWebService objService = new MyWebService();
 
     //Set the callback method for the async operation
     objService.SaveDataCompleted += new SaveDataCompletedEventHandler(objService_SaveDataCompleted);

    objService.SaveDataAsync(someDataHere);

    //This should ONLY return True if the save was successful!
    return true;
}

void objService_SaveDataCompleted(object sender, SaveDataCompletedEventArgs e)
{
      if (e.Errors == null)
      {
          //At this point, the Save() method could return TRUE
          MessageBox.Show("Save was successful!");
      }
     else
     {
         //At this point, I'd want the Save() method to return FALSE
         MessageBox.Show("Save was NOT successful");
     }        
}