Bring window to front when it is shown (Caliburn.Micro)

I hope you can help me with my problem.

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What is the situation:

I'm working on a C# WPF application with the MVVM patte. I'm using Calibu.Micro and MahApps.Metro.

I have a list of ViewModels in ViewModelA:

ObservableCollection<ViewModelB> ViewModelList { get; set; }  // short version

There is a ListView in my corresponding View that binds to this list:

<ListView ItemsSource="{Binding ViewModelList}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <Grid>
                <ContentControl cal:View.Model="{Binding }" />
            </Grid>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

The ViewModels in the list are displayed by a ContentControl.

In ViewModelB there is an event that gets called on a double click on the corresponding View (MetroWindow):

public void OnDoubleClick()
{
    var windowManager = IoC.Get<IWindowManager>();
    windowManager.ShowWindow(new ViewModelC());
}

The WindowManager shows a new non modal window for me (View of ViewModelC).

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What is the problem:

The non modal window is not focused and behind my main window after it's shown by WindowManager.

I tried a lot of settings for my window like ShowActivated, Owner, Topmost... When I set the owner to my main window then the shown window behaves like Topmost is set to true.

I just want the window to appear on front of my main window (not Topmost=true) and focused.

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Unsatisfying solution:

I can replace the ContentControl with the View I want to display and get rid of the list of ViewModels. If I do that I can listen to the MouseDoubleClick event of my ListView and get the selected element with the property SelectedIndex.

If I do it that way the shown window behaves like I want it to (on top, focused).

But ViewModelB needs a lot of logic and I want to encapsulate it.

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It would be really great if someone can solve my problem.

Best regards, mash