believe it or not - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
It's true, whether or not you agree, as in Believe it or not, I finally finished painting the house. Originating in the 1800s, this phrase gained currency as the title of a cartoon series begun in 1918 by Robert Ripley and continuing to run in American newspapers long after his death in 1949. Each drawing presented a strange but supposedly true phenomenon, such as a two-headed chicken.