@Dimitris The OP might have been confused by the non negligible number of occurrences of il est retard Google returns. I even found one in the "Grevisse de l'étudiant" 2017, missed by proofreaders... The expression is nevertheless invalid. While the en is unstressed and often no more nasalized (il est a r'tard), it is still there.

@jlliagre Thank you very much! I am working on improving my answer:-!)

@jlliagre Je viens de modifier ma réponse ; j'espère l'avoir améliorée:-)! Merci encore !