New Post: CheckListBox: Current Active Item

I have a CheckListbox and a label/Textblock.

<xctk:CheckListBox HorizontalAlignment="Left" Margin="20,38,0,94" Name="clbItems" Width="256" 
                           ItemsSource="{Binding ItemsReference,ElementName=AllocatingCheckListBoxControl}"
                           DisplayMemberPath="{Binding DisplayMemberReference, ElementName=AllocatingCheckListBoxControl}"
                           ValueMemberPath="{Binding ItemsReferenceIdColumnName, ElementName=AllocatingCheckListBoxControl}"/>
        
        <Label HorizontalAlignment="Left" Margin="20,0,0,24" Name="lblDescription" Width="256" Height="64" VerticalAlignment="Bottom">
                <TextBlock Text="{Binding UserGroupRoleDescription}" DataContext="{Binding ElementName=clbItems, Path=SelectedItem}"
                           TextWrapping="Wrap" />

The Label should be filled when the user select a item. Now the text will be only shown, when the user check the item. If he uncheck the item, then the textblock text will be empty

What is the property of the current active Item in the CheckListBox?