Lo and behold
Definition 1 of 1
Pro Tip 1/3Expressing Awe
Use 'lo and behold' to show you're amazed by an unexpected discovery or event. 
I opened the old book, and lo and behold, a hidden letter fell out.
Pro Tip 2/3Archaic Flavor
'Lo and behold' adds a quaint or old-fashioned tone to modern speech or writing. 
We turned the corner, and lo and behold, there stood a castle straight out of a fairy tale.
Pro Tip 3/3Dramatic Reveal
It's often used to dramatize the moment something surprising is revealed. 
They said it was sold out, but lo and behold, one last ticket was available!