Where did this email address come from?

Could anyone please help me? I went to log into facebook through my internet browser on my iphone, and when I entered facebook.com, a random email address was already filled into the username/email block. The email was my first name.last [email protected]. I have honestly never seen this email address before and now my wife thinks I have a secret email account for facebook. Does Facebook automatically generate random emails with your first and last name from your account? I can't find any info online about it. Please someone help!