GridView Items does not have same height - user-interface

Question

I have a GridView that displays Header and Sub-Items like so:
<GridView ItemsSource="{Binding Path=MainViewModels}">
<GridView.ItemTemplate>
<DataTemplate>
<Grid VerticalAlignment="Top">
<Grid.RowDefinitions>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Border BorderBrush="White" BorderThickness="1"></Border>
<Grid VerticalAlignment="Top" HorizontalAlignment="Left">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Border Grid.Row="0" BorderBrush="White" BorderThickness="1"></Border>
<TextBlock Grid.Row="0"
HorizontalAlignment="Left"
Foreground="#FFAAAAAA"
Style="{StaticResource Style_TextBlock_Label_H3}"
Text="{Binding Path=Description}" VerticalAlignment="Top" />
<GridView Grid.Row="1"
ItemsSource="{Binding Path=SubViewModels}">
<GridView.ItemTemplate>
<DataTemplate>
<TextBlock Margin="0,0,5,0"
Text="{Binding Path=Description}"
TextWrapping="Wrap" />
</DataTemplate>
</GridView.ItemTemplate>
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<WrapGrid Orientation="Vertical" VerticalAlignment="Stretch" />
</ItemsPanelTemplate>
</GridView.ItemsPanel>
</GridView>
</Grid>
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"
VerticalAlignment="Top">
</StackPanel>
</ItemsPanelTemplate>
</GridView.ItemsPanel>
</GridView>
However, whenever it renders, it renders like this:
What I want to achieve is that all the "Header" are on the top, while the Items themselves extend to the bottom and then just overflow using the WrapGrid.
Can please point out where I am going wrong?
Thank you!