Well that is what cuss words are for....
More information would be helpful but 1st things that come to mind......
Where did it break?
Is there a sharp edge on your bridge? (not sure which type of bridge but it could even be the edge of a string hole)
I know it sounds stupid but it does happen...are you sure you are tuning to the right E and not an octave higher?
Did you accidentally grab the wrong string? (again it sounds stupid but it is not unheard of as all it takes is one little distraction)
What type of strings are you using?
I prefer Worth Browns these days but everyone has their preference that way....