Symfony 2.8 - display certain entity value in form field widget template

I am building a custom file upload widget where I display last uploaded filename. I created FormType class and in form/fields.html.twig I added the following:

{% block custom_document_widget %}
    {% spaceless %}
        {# here I want to include code to display filename #}

        {# display file input #}
        {% set type = 'file' %}
        {{ block('form_widget_simple') }}
    {% endspaceless %}
{% endblock %}

I know that the value of a current field can be parsed {{ form.vars.value }}, but in the end the field is file input and does not have the value of filename that was uploaded previously.

To store uploaded filename I have $filename variable in entity and would like to display it in field widget template. How can I approach it?

In the end I had to pass the filename as an option to embedded form that represented my FileType:

$builder
    ->add('resumeFile', CustomDocsType::class, array(
        'required' => false,
        'constraints' => array(
            new File(array(
                'mimeTypes' => array(
                    'application/pdf',
                ),
                'mimeTypesMessage' => 'mimetype',
            )),
        ),
        'filename' => $trainee->getResumeOriginal(),
    ))

In my CustomDocsType:

class CustomDocsType extends AbstractType
{
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        parent::buildView($view, $form, $options);

        $view->vars = array_merge($view->vars, array(
            'filename' => $options['filename']
        ));
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'filename' => null
        ));
    }

    public function getParent()
    {
        return FileType::class;
    }
}

And now I only had to acces the filename in template:

{{ form.vars.filename }}