How to get TabPanel ActualWidth from TabControl - wpf

Question

I have a tabcontrol and tab strip placement is on left. So it is a simple navigation menu type tab control.
There is a TabPanel inside TabControl's control template.
<ControlTemplate TargetType="{x:Type TabControl}">
<Grid x:Name="Grid" ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
<Grid.ColumnDefinitions>
<ColumnDefinition x:Name="ColumnDefinition0"/>
<ColumnDefinition x:Name="ColumnDefinition1" Width="0"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition x:Name="RowDefinition0" Height="Auto"/>
<RowDefinition x:Name="RowDefinition1" Height="*"/>
</Grid.RowDefinitions>
<Border x:Name="ContentPanel" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="0" KeyboardNavigation.DirectionalNavigation="Contained" Grid.Row="1" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local" Padding="{TemplateBinding Padding}" Margin="0,-1,0,0">
<ContentPresenter x:Name="PART_SelectedContentHost" ContentSource="SelectedContent" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</Border>
<ScrollViewer x:Name="scroll" VerticalScrollBarVisibility="Disabled" HorizontalScrollBarVisibility="Auto" Template="{StaticResource ScrollViewerTab}">
<TabPanel x:Name="HeaderPanel" IsItemsHost="true" Margin="0,2,0,0" KeyboardNavigation.TabIndex="1" Panel.ZIndex="1" VerticalAlignment="Bottom" />
</ScrollViewer>
</Grid>
</ControlTemplate>
I need TabPanel's (tab headers) ActualWidth outside tabcontrol for alignment purposes.
I tried following but it did not work.
<TextBlock Text="{Binding Path=Actualwidth, ElementName=HeaderPanel}" />
<TabControl />
I also tried to bind the ActualWidth of header panel to Tag property of TabControl. Even that did not work.
<TabControl Tag="{Binding Path=ActualWidth, ElementName=HeaderPanel}" />
TabControls.Items collection gives the list of ViewModel objects. So I cannot get TabItem instances.

Answer 1

I ended up using visual tree helper in the codebehind file
var tabPanel = VisualTreeHelpers.FindChild<TabPanel>(TabControl, "MenuPanel");