def tell_domain_tls_name(d):
    """
    >>> tell_domain_tls_name('*.example.com')
    'example-com'
    >>> tell_domain_tls_name('prometheus.example.com')
    'prometheus-example-com'
    """
    parts = d.split('.')
    if parts[0] == '*':
        parts = parts[1:]

    return '-'.join(parts)