expression
not only that but also; that goes without saying, but also
Used to acknowledge a preceding point while adding another, often more important, point. Functions as a conjunctive expression.
彼は才能があるのはさることながら、努力も惜しまない。
Not only is he talented, but he also spares no effort.
このレストランは味が良いのはさることながら、サービスも素晴らしい。
Not only is the food good at this restaurant, but the service is also excellent.
A common variant with the particle も, emphasizing 'also' or 'as well'. さることながら can be used without も, but もさることながら is more frequent.
From 然る (さる, 'such') + 事 (こと, 'thing') + ながら ('while, although'). Literally 'while it is such a thing', it developed into a set phrase meaning 'not only that but also'.