WPF: Spilt GridView header into two rows where the bottom row is seperated into two colums

<GridViewColumnHeader>
    <GridViewColumnHeader.Template>
        <ControlTemplate>
            <Grid VerticalAlignment="Center" HorizontalAlignment="Center">
                <Grid ShowGridLines="False" VerticalAlignment="Center" HorizontalAlignment="Center">
                    <Grid.RowDefinitions>
                        <RowDefinition Height="*"/>
                        <RowDefinition Height="*"/>
                    </Grid.RowDefinitions>
                    <TextBlock Grid.Row="0" Text="SomeHeaderText" HorizontalAlignment="Center"/>
                    <Grid Grid.Row="1">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*"/>
                            <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <TextBlock Grid.Column="0" Text="SubHeaderText1" Padding="5"  HorizontalAlignment="Center" />
                            <TextBlock Grid.Column="1" Text="SubHeaderText1" Padding="5" HorizontalAlignment="Center" />
                        </Grid>
                    </Grid>
            </Grid>
        </ControlTemplate>
    </GridViewColumnHeader.Template>
</GridViewColumnHeader>

<GridViewColumnHeader>
   <Grid HorizontalAlignment="Center" VerticalAlignment="Center">
      <Grid HorizontalAlignment="Center" VerticalAlignment="Center" ShowGridLines="False">
         <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
         </Grid.RowDefinitions>
         <TextBlock Grid.Row="0" HorizontalAlignment="Center" Text="SomeHeaderText"/>
         <Grid Grid.Row="1">
            <Grid.ColumnDefinitions>
               <ColumnDefinition Width="*"/>
               <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <TextBlock
               Grid.Column="0"
               HorizontalAlignment="Center"
               Padding="5"
               Text="SubHeaderText1"/>
            <TextBlock
               Grid.Column="1"
               HorizontalAlignment="Center"
               Padding="5"
               Text="SubHeaderText1"/>
         </Grid>
      </Grid>
   </Grid>
</GridViewColumnHeader>