Can anyone help me with an accurate English to Latin translation?

Question

Hi,

My family motto is "Loyalty without defect", and was originally in Latin. However I have lost the original and now can only remember the English version.

I am aware, however, that Latin is quite complex. I would like to avoid using any of the auto translators as they just provide a word for word translation that does not really work in Latin. Is there a Latin Pro out there who can help?

Answer 1

This motto is an old french one -Loyauté sans tache  

Answer 2

Fides (or Fidelitas) sine vitio

or also

Fides (or Fidelitas) sine culpa

Answer 3

Your last name isn't Mountbatten-Windsor is it? I can't imagine why someone would have a family motto unless they were royalty...