i want to load an event on loading each dot but the event is called before the page appears

Question

I'm new to WPF and using the loading animation i want to load the event on the dot changed of animation I tried a lot but the event loads before the window appears.

<StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center">
    <StackPanel.Triggers>
        <EventTrigger RoutedEvent="Rectangle.Loaded">
            <BeginStoryboard>
                <Storyboard Name="waitingAnimation" RepeatBehavior="1x" >
                    <DoubleAnimation Storyboard.TargetName="Dot1" BeginTime="0:0:0.0" Storyboard.TargetProperty="Opacity" From=".1" To="1" AutoReverse="False" Duration="0:0:5.0"/>
                    <DoubleAnimation Storyboard.TargetName="Dot2" BeginTime="0:0:5.0" Storyboard.TargetProperty="Opacity" From=".1" To="1" AutoReverse="False" Duration="0:0:5.0"  />
                    <DoubleAnimation Storyboard.TargetName="Dot3" BeginTime="0:0:10.0" Storyboard.TargetProperty="Opacity" From=".1" To="1" AutoReverse="False" Duration="0:0:5.0"  />
                    <DoubleAnimation Storyboard.TargetName="Dot4" BeginTime="0:0:15.0" Storyboard.TargetProperty="Opacity" From=".1" To="1" AutoReverse="False" Duration="0:0:5.0"/>
                    <DoubleAnimation Storyboard.TargetName="Dot5" BeginTime="0:0:20.0" Storyboard.TargetProperty="Opacity" From=".1" To="1" AutoReverse="False" Duration="0:0:5.0"/>
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </StackPanel.Triggers>
    <Ellipse Name="Dot1" Fill="White" Opacity=".1" Width="8" Height="8" />
    <Ellipse Name="Dot2" Fill="White" Opacity=".1" Width="8" Height="8" Margin="2,0,0,0" />
    <Ellipse Name="Dot3" Fill="White" Opacity=".1" Width="8" Height="8" Margin="2,0,0,0"/>
    <Ellipse Name="Dot4" Fill="White" Opacity=".1" Width="8" Height="8" Margin="2,0,0,0" Loaded="Dot4_Loaded"/>
    <Ellipse Name="Dot5" Fill="White" Opacity=".1" Width="8" Height="8" Margin="2,0,0,0"/>
</StackPanel>

Code behind:

public StartUp()
{
    InitializeComponent();
    this.WindowState = WindowState.Maximized;
}

private void Dot4_Loaded(object sender, RoutedEventArgs e)
{
    MessageBox.Show("Hi");
}