zhèng​qiǎo

by chance

正巧 zhèng​qiǎo
by chance adverb
to occur by coincidence at a specific moment; to happen to

When I went to the bookstore, I happened to run into my teacher.

opportune adverb
occurring at a particularly convenient or favorable time

I was just about to head to the station when you called; the timing was perfect.

Frequency

Movie subtitles
2.41 per million appears in 1% of films
Written text
1.72 per million

Sources

Definitions
CC-CEDICT