Can a TextBlock in a Flyout have wrapped text?

The TextBlock in the following code does not wrap.

<AppBarButton x:Name="abbFooHelp" Icon="Help" IsCompact="True" VerticalAlignment="Center" HorizontalAlignment="Center">
    <AppBarButton.Flyout>
        <Flyout>
            <TextBlock TextWrapping="Wrap">This is a very looooooooooooooooooooog text. This is a very looooooooooooooooooooog text.</TextBlock>
        </Flyout>
    </AppBarButton.Flyout>
</AppBarButton>

Could any one offer a tip?

---

Hong