McDonald's admits it copied the idea for an ad campaign from a series of photos that went viral a month ago

McDonald's has apologized to a pair of freelancers who accused the fast food chain of stealing their idea in a recent marketing campaign, Adweek reports.

Kristina Bakrevski's photos of writer David Sikorski in a mock engagement photo montage with a burrito went viral last month after they were published in BuzzFeed, then picked up in other news outlets such as The Huffington Post and People.

On August 3 McDonald's launched a Twitter marketing campaign for McDonald's $2.50 double cheeseburger combo deal. Not only did they carry a mock engagement theme, but the photos strongly resembled Bakrevski and Sikorski's montage.

McDonald's sent this statement to Adweek: "This shouldn't have happened and, with our agency partner, we're working to find out how it did. We're reaching out to David Sikorski and Kristina Bakrevski. We apologize to them, their fans and ours."

McDonald's has now removed the five images from its Twitter feed.

Sikorski told Business Insider on Thursday that he had contacted a licensing lawyer and is exploring taking legal action against McDonald's.

Here's one of Sikorski and Bakrevski's original images.

And here's one of McDonald's images.

Another image from the viral photo montage.

McDonald's tweet looked very similar.

Another of the original photos.

McDonald's also photographed a mock engagement on a park bench.