Lo and behold
An exclamation, on drawing others attention to something. Used especially to to announce things that are considered startling or important. The phrase is often written with an exclamation mark.
The word 'lo' as used in this phrase is a shortening of 'look'. So, lo and behold! has the meaning of look! - behold!. Lo in this and its other meaning, which is more akin to O!, has been in use since the first Millennium and appears in the epic poem Beowulf.
Something not very far removed from lo and behold appears in the Bible, Genesis 15:3 (King James Version):
"And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir."
The complete phrase is first recorded in an 1808 letter in the Correspondence 1787–1870, of Queen Victoria's lady of the bedchamber - Lady Sarah Spencer Lyttelton:
"Hartington... had just told us how hard he had worked all the morning... when, lo and behold! M. Deshayes himself appeared."