Change TabItem's Header FontWeight - wpf

Question

I would like to change the TabItem's Header FontWeight to Bold when IsSelected = True from my ResourceDictionary.
Some Code
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TabItem}">
<Grid>
<Border Name="Border"
Background="White"
BorderBrush="White"
BorderThickness="1,1,1,0"
Margin="0,0,0,-1" >
<ContentPresenter x:Name="ContentSite"
Height="25"
VerticalAlignment="Bottom"
HorizontalAlignment="Center"
ContentSource="Header"
Margin="12,2,12,2"/>
</Border>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter TargetName="Border" Property="Background" Value="#F2F1F0" />
<Setter TargetName="Border" Property="BorderBrush" Value="Gray" />
<Setter TargetName="Border" Property="BorderThickness" Value="0.5,0.7,0.5,0" />
<Setter Property="Header">
<Setter.Value>
<TextBlock Text="{Binding Path=Header.Title, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TabItem}}}"
FontWeight="Bold" />
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsSelected" Value="False">
<Setter TargetName="Border" Property="Background" Value="White" />
<Setter TargetName="Border" Property="BorderBrush" Value="Gray" />
<Setter TargetName="Border" Property="BorderThickness" Value="0,0,0,0.5" />
</Trigger>
.....etc.....
The above approach doesn't work. Also setting the HeaderTemplate instead of Header it works but it ruins my template. Finally, setting the TextBlock.FontWeight as a Property inside the Trigger changes all the TextBlocks inside the TabItem.
Any Proposals?
UPDATE
I picked up #ShineKing answer because it helped me solve my problem. Basically what i did is add a DataTrigger to the TextBlock used as a Header to my "custom" TabItem.
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding Path=IsSelected, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TabItem}}}" Value="True">
<Setter Property="FontWeight" Value="Bold"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>

Answer 1

Could you try this code to change TextBlock as Bold
<TabControl>
<TabControl.Resources>
<Style TargetType="TextBlock" x:Key="HeaderTextBlockStyle">
<Style.Triggers>
<DataTrigger Binding="{Binding IsSelected,
RelativeSource={RelativeSource AncestorType=TabItem}}"
Value="True">
<Setter Property="FontWeight" Value="Bold"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TabControl.Resources>
<TabItem>
<TabItem.Header>
<TextBlock Text="Header Text"
Style="{StaticResource HeaderTextBlockStyle}"/>
</TabItem.Header>
</TabItem>
</TabControl>