勿怪の幸い

もっけのさいわい【勿怪の幸い】

an unlooked-for piece of luck; a piece [stroke] of good luck; a piece of good fortune; a godsend; a windfall.

●任地があなたと同じシンガポールになったのはもっけの幸いでした. It was a happy coincidence [by pure, undeserved luck] that I was posted to Singapore at the same time as you were.

・そこで彼に出会ったのはもっけの幸いだった. It was by a stroke of good luck [It was really providential] that I met him there. | I found him there by pure luck.