Grid layout and expanding controls (TextBox) - wpf

Question

I seem to not understand the layout behavior in my application. In the following sketch I have a TextBox that expands as text is being entered. How can I prevent that from happening and have the Height stay constant and get a Scrollbar instead? The size of the right TextBox should the size the left three TextBoxes take.
Initial state:
After adding several values:
Here's the XAML:
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid Grid.Row="0" Background="LightBlue">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBox Grid.Row="0" Grid.Column="0" Text="One" Margin="5" />
<TextBox Grid.Row="1" Grid.Column="0" Text="Two" Margin="5" />
<TextBox Grid.Row="2" Grid.Column="0" Text="Three" Margin="5" />
<TextBox
Grid.RowSpan="3" Grid.Column="1" Margin="5"
AcceptsReturn="True"
Text="Hello World!"
VerticalScrollBarVisibility="Auto"
/>
</Grid>
<Rectangle Grid.Row="1" Fill="Blue" />
</Grid>

Answer 1

Simple Answer
Assuming that the font size and margins of the TextBoxes are going to remain constant, and that the TextBoxes on the left are single-line only, you can just set a fixed height for the top RowDefinition:
<Grid.RowDefinitions>
<RowDefinition Height="84" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
Complicated Answer
If the left TextBoxes are multiline, or if the font size or margins can change, then you'll have to get a bit more complicated. I don't think there's an existing Panel that can handle that, you'd have to manually set the Height of the right TextBox to match the sum of the ActualHeight + Margin.Top + Margin.Bottom for all of the left TextBoxes. This would need to be done whenever SizeChanged was raised on any of the left TextBoxes.