Something surprising happened to me, so I decided to look through some old photos...
この場合、次のように言うと良いですよ。
ーSomething surprising happened to me the other day, so I decided to look through some old photos. When I was looking at all the pictures, I found one that I had taken of the city and you were in it. What was even stranger was that we hadn't even met at that point.
「先日驚くことがあって、昔の写真に目を通していたら、街並みを撮った写真にあなたが写っているのを見つけました。何がもっとおかしいかというと、その時点で私たちはまだ出会っていなかったということです」
Something surprising happened to me で「驚くことがあった」と言えます。
to look through some old photos「古い写真に目を通す」
ご参考まで!