A couple had their engagement picture photobombed by an adorable baby hippo – and the pictures are priceless.

According to The Telegraph, Nick Kelble and his girlfriend Hayley Roll have been followers of Fiona the hippo at the Cincinnati Zoo in Ohio since she was born – so they were happy to share the special moment with her on October 8.

Roll posted a series of photos of the event on her Instagram page, with the caption: “We’re so happy Fiona could be there on our special day,” adding: “Here’s to many more years of going to zoos with you.”

She told The Daily Buzz that the couple had gone to the zoo for their one-year anniversary, and Fiona had been in the window.

“Nick, my boyfriend, and I were waiting in line to get our photo taken with Fiona and I gave my cell phone to someone to take the photo and when I turned back around, Nick was on one knee proposing,” she said.

You can scroll through the engagement photos below:

http://instagr.am/p/BZ_usKJBZKY

Roll said that nobody at the Zoo knew about the engagement - or the epic photo.

The Telegraph reported that Fiona was the first Nile hippo born at the zoo in 75 years back in January, and had a fight to survive after being born six weeks premature.

The Zoo called her a "little hippo with a big personality."

"Full term hippos usually weigh between 50-110lbs," the zoo told The Telegraph. "Fiona only weighed 29lbs when she was born 6 weeks premature. She is the smallest hippo to ever survive." "As Fiona continues to grow, the many facets of her complex personality are really starting to show!"