The President of Liberty University was at the centre of a social media backlash this week over a photo of himself in which his trousers were unzipped. 

Jerry Falwell Jr's underwear was visible in the since-deleted photo of him posing at a costume party on a yacht. 

The photo showed him with his trousers unzipped and his T-shirt rolled up, exposing his midrift. He had his arm around his wife's pregnant assistant, whose shorts were also unzipped. 

The shot was taken while Falwell was on vacation with his wife. He posted the picture to Instagram but deleted it after numerous posts criticized it. 

The picture was widely circulated after Robert Downen, religion reporter for The Houston Chronicle, tweeted it with the caption "wut is happening [sic]".

He attempted to explain the context of the photo in an interview with radio show "MorningLine" on WNLI.

"She's pregnant, so she couldn't get her pants zipped," he said.

"I had on a pair of jeans I haven't worn in a long time, so I couldn't get mine zipped up, either. And so, I just put my belly out like hers."

He then said he "should never have put it up" and has since "apologized to everybody."

"I promised my kids I'm going to try to be better," he added. "I'm going to be a good boy from here on out ... it was just good fun, that's it."