How to initialize formset in Django admin?

Question

Django

There are two models:

Post

class Post(models.Model):
    title = models.CharField(max_length=150, db_index=True, verbose_name='Заголовок')
    body = models.TextField(verbose_name='Текст поста')
    author = models.ForeignKey(AdvancedUser, on_delete=models.PROTECT, verbose_name='Автор', related_name='posts')
    post_date = models.DateTimeField(auto_now=True, verbose_name='Дата публикации')

    def __str__(self):
        return self.title

    class Meta:
        verbose_name = 'Пост'
        verbose_name_plural = 'Посты'
        ordering = ('-post_date',)

and

Comment

class Comment(models.Model):
    post = models.ForeignKey(Post, on_delete=models.CASCADE, verbose_name='Пост')
    author = models.ForeignKey(AdvancedUser, on_delete=models.PROTECT, verbose_name='Автор')
    comment_date = models.DateTimeField(auto_now_add=True, verbose_name='Дата комментария')
    comment_text = models.TextField(verbose_name='Комментарий', help_text='Допускается использование HTML разметки.')

    def __str__(self):
        return f'Comment to {self.post} post'

    class Meta:
        ordering = ('comment_date',)

related ForeignKeys.

The comment has an author.
In the admin panel, I display the post editing form and the formset to it with the comments left.
How can I initialize the "Author" field in the formset only for a new comment with the name of the current logged in user, while not changing this field for already existing comments?

screenshot