The photos have now garnered over 28,000 retweets and nearly 83,000 likes.
She talked to magazine's Select All via direct messages on Twitter.
The incident occurred while Henry was standing knee-deep in a beautiful river near her hometown of Eugene, OR.
Her friend Elena was snapping some shots to commemorate Henry entering her senior year of high school.
Jillian Henry, 17, a senior at South Eugene High School in Oregon, was being photographed by her friend Elena Nesbit on Saturday when she noticed the potbellied nudist appear in the Willamette River near Mount Pisgah.
The long-haired blonde, clad in a black dress, smiled as she glanced over at the interloper and his dog as they stood nonchalantly in the water.
"We were taking some [photos] in the water when we realized he was a few spots down, naked, and we started laughing so hard," she told the site.
This high school student could barely contain her amusement while posing for her senior picture – when she was photobombed by the nudist and his pooch.
Everybody loves a good photobomb, especially one that unintentionally involves nudity.
That's exactly the situation in which high school senior Jillian Henry found herself during a lovely outdoor photo shoot with a friend.
“Love my senior pics,” Henry tweeted along with a bashful, smiling emoji.
Incidentally, a butt-naked and blissfully unaware man and his dog were milling in the background.
Henry tweeted out a couple of the shots, which quickly went viral.