It was an unfortunate accident.

那是一次不幸的事故。

《牛津词典》

Suffered an unfortunate accident.

遭遇到不幸的事故。

youdao

By that time everyone will have forgotten this unfortunate accident.

不过那时人们早就忘却这起不幸的事件了。

youdao

So a really miraculous outcome to what could have been a very, very unfortunate accident.

CNN: Ryan Chilcote: First deep attack

"This was in our opinion an unfortunate accident for which a prosecution was wholly unjustified, " she said.

BBC: Legoland Windsor fined after worker fell from ride

"I feel that we are fortunate that even more injuries were not the result of this very tragic and unfortunate accident, " said U.S. Sen.

WSJ: Probe into Conn. train crash giving way to cleanup