yī​qù​bù​fù​fǎn

gone forever

一去不复返 (一去不復返) yī​qù​bù​fù​fǎn
gone forever adverb
gone and never to return; gone forever

青春一去不复返

qīng​chūn yī​qù​bù​fù​fǎn.

Youth, once gone, never returns.

Frequency

Movie subtitles
1.52 per million appears in 1% of films
Written text
1.79 per million

Sources

Definitions
CC-CEDICT