cannot display classes of courses

I am trying to create an educational website using django, so I have two models class and course which have a one-to-many foreignkey relationship between them i.e. one course can have several class but one class can only have one course. But this creates a problem for me. That is, in my course_detail_view I have assigned the model course. So I cannot render classes in my html file. Can anyone help me solve this ?

My models.py:

class Course(models.Model):
    title = models.CharField(max_length=100)
    image = models.ImageField(upload_to='class/instructor_pics', null=True)
    instructor = models.CharField(max_length=100)
    instructor_image = models.ImageField(upload_to='class/instructor_pics', null=True)
    students = models.ManyToManyField(User, related_name='courses_joined', blank=True)

    slug = models.SlugField(max_length=200, unique=True)
    description = models.TextField(max_length=300, null=True)
    created = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['-created']

    def __str__(self):
        return self.title

class Class(models.Model):
    title = models.CharField(max_length=100)
    video = models.FileField(upload_to='class/class_videos',null=True,
validators=[FileExtensionValidator(allowed_extensions=['MOV','avi','mp4','webm','mkv'])])
    course = models.ForeignKey(Course, on_delete=models.CASCADE, null=True, related_name='classes')


def __str__(self):
    return self.title

My views.py:

class CourseDetailView(LoginRequiredMixin, DetailView):
    model = Course
    template_name = 'class/course.html'

Thanks in advance!