They met by chance.

他们不期而遇。

《牛津词典》

Although we have only met by chance, I can see you are a very remarkable girl with a clear purpose in life.

虽然我们萍水相逢，可是我觉得你是个了不起的有志气的姑娘。

《新英汉大辞典》

I believe this is met by chance, then I accidentally forget.

我相信这是偶然的相遇，然后我偶然的忘记。

youdao

Jamelle and Karane said they hit it off immediately after they met by chance at a downtown club's Ladies Night, and felt like they had known each other forever.

CNN: Married same-sex couple awaits epic high court appeal

Mr Coats told the court that he travelled almost daily down to West Kilbride to see her between 14 and 26 April and was told by Smith and Parker three days later, when he met them by chance in Largs, that she had left and gone to Dumfries.

BBC: Lynda Spence

The student met the trio by chance as he ate in Krunchy Fried Chicken takeaway in Fallowfield after enjoying a night out with fellow students at a city centre bar.

BBC: Daniel Whiteley