it is regrettable that ...; it's a pity that ...; unfortunately, ...
A formal, somewhat literary expression used to introduce a statement of regret or disappointment. Often found in written Japanese or formal speech.
It is regrettable that his talent was not fully utilized.
惜しむらくは、天候に恵まれず、せっかくの景色が楽しめなかった。
Unfortunately, the weather didn't cooperate, and we couldn't enjoy the scenery we had come for.