tabcontrol inside radwindow

[NS]

Hello,
My Radwindow is declared as follow:

<telerik:RadWindow x:Name="window" ResizeMode="NoResize" Width="500" Height="300" Header="User Information" WindowStartupLocation="CenterScreen" LeftOffset="-150" TopOffset="-50" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
            <ADTool:ADUserDetail x:Name="usrCtrlUserDetail" />
        </telerik:RadWindow>

ADUserDetail contains the following code (including tabcontrol)

<UserControl x:Class="SilverlightADTool.ADUserDetail"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:telerik="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Navigation"
    d:DesignWidth="1024" d:DesignHeight="768"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d">
    <Grid x:Name="LayoutRoot" Background="White" Width="Auto" Height="Auto" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        <Grid.RowDefinitions>
            <RowDefinition Height="0.062*"/>
        </Grid.RowDefinitions>
        <telerik:RadTabControl HorizontalAlignment="Stretch" Margin="0,0,0,8" x:Name="rtcHeader" VerticalAlignment="Stretch">
            <telerik:RadTabItem Header="User Information">
                 <Grid x:Name="LayoutRoot2" Background="White">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="124"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="31"/>
            <RowDefinition Height="29" x:Name="rowAspex"/>
            <RowDefinition Height="29"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <TextBlock Margin="8,2,17,8" Text="ASPEX User" TextWrapping="Wrap" Grid.Row="1"/>
        <TextBox HorizontalAlignment="Left" Margin="8,3.5,0,5.5" Width="199" Grid.Column="1" Text="TextBox" TextWrapping="Wrap" Grid.Row="1" VerticalAlignment="Stretch" Height="20" x:Name="txtbAspexUser"/>
        <TextBlock Margin="8,8,17,8" Text="ASPEX User" TextWrapping="Wrap" Grid.Row="2"/>
        <TextBlock HorizontalAlignment="Stretch" Margin="9,6,-94,2" Width="Auto" Text="" TextWrapping="Wrap" x:Name="txtbUserName" FontFamily="Aharoni" FontSize="16" Grid.Column="1"/>

    </Grid>
            </telerik:RadTabItem>
            <telerik:RadTabItem Header="Group Membership">
                <TextBlock Text="test group membership" />
            </telerik:RadTabItem>
        </telerik:RadTabControl>
    </Grid>
</UserControl>

Problem is that the Tabcontrol doesn't stretches to the right of the RadWindow.
I want to when I resize the Radwindow that the Tabcontrol automatically is attached to the right of the RadWindow.

How can I do this ?

[NS]

Found the solution myself :)

I must set the Width and Height of the usercontrol inside the radwindow to the width and height of the radwindow.

I also use the SizeChanged event of the radwindow to update the width and height of the usercontrol to the width and height of the radwindow.