。
In my whole life, I have not one regret.
Literal
My [genitive-の] lifetime [at-に] one-fragment [genitive-の] regret not-exist.
A declamatory statement in classical register. Most famously the dying words of Raoh from the manga 北斗の拳 (Fist of the North Star). 我が (わが) is the formal/classical possessive for 'my' (also seen in set phrases like 我が国 'our country'). 生涯 ('lifetime, life span') is a formal noun for the full arc of one's life. 一片 ('one fragment, a single piece') is a literary quantifier, used for things usually measured in smaller units — a piece of hope, a fragment of cloud, a speck of regret. 悔い ('regret') is the classical/literary noun form of 悔いる ('to regret'). 無し ('not exist') is the classical predicative form of ない. Every piece of the sentence signals elevated, almost heroic register.