Retrieve selected value from templated datagrid comboboxcolumn in WPF

Hi EE,
    I recently moved from winform to WPF, so bear with me if my question sounds a bit weird as I realised there's a bit learning curve trying to adopt the changes.

   anyways, I'm trying to use a datagrid control, which has a combobox column, I created template for the combobox to have both Image and person Name showing inside it (Binding works ok), however I found its impossible to get the combox's selected value, i.e. User selects one person, after a button click, I'd like to grab that person's name, how would I do that in WPF?

   Datagrid is binding to an object list of (PersonEvent), Combobox is binding to an object list of (Person), List of Person is a property of PersonEvent.

Xaml like this:

<DataGridTextColumn   Binding="{Binding EventNumber}" MinWidth="90" IsReadOnly="True" Header="Event Number"
                                              HeaderStyle ="{StaticResource DgvHeaderStyle}" ElementStyle="{StaticResource DgvTextCellStyle}" />

                        <DataGridTemplateColumn   Header="Person"  MinWidth="160" HeaderStyle="{StaticResource DgvHeaderStyle}" >
                            <DataGridTemplateColumn.CellTemplate>
                                <DataTemplate>
                                    <ComboBox x:Name="cbPerson"  ItemsSource="{Binding Person}"  SelectedValuePath="PersonName"    >
                                        
                                        <ComboBox.ItemTemplate>
                                            <DataTemplate>
                                                <StackPanel Orientation="Horizontal">
                                                    <Image x:Name="imgPerson" Width="60"  Height="60" Stretch="Fill" Source="{Binding Photo, Converter={StaticResource nullImageConverter}}" />
                                                    <TextBlock x:Name="tbPerson" Text="{Binding PersonName}" Margin="5,0,0,0"/>
                                                </StackPanel>
                                            </DataTemplate>
                                        </ComboBox.ItemTemplate>
                                    </ComboBox>
                                </DataTemplate>
                            </DataGridTemplateColumn.CellTemplate>
                        </DataGridTemplateColumn>

Select allOpen in new window

in vb file i set itemssource to datagrid:

Dim PersonEvent as new ObservableCollection(Of PE)
'Populate the list'
dgv.Itemssource = PersonEvent

Select allOpen in new window

Above displaying all working fine, but I'm struggling to get 'cbPerson' selected value as I cant reference this combobox in code, is there a solution to this ? or is there a better way of doing what I'm trying to do?