A Marine whose bike was stolen while in Colorado posted a calm but scathing plea on social media for its return.

Robert Kugler and his chocolate lab Bella were thrust into internet fame when the pair embarked on an Instagram-worthy road trip earlier this summer. Bella was diagnosed with cancer in 2015 and given just a few months to live, so Kugler decided to take to the road and make his best friend's last days her best days.

Now, more than a year after her diagnosis, Kugler says his irreplaceable bike was stolen from the back of his 4Runner while he was in Fort Collins.

"The first thing I thought was I should have had it locked up better myself," said Kugler. "The second thought is it's just not fair I should be thinking I should lock my own thing up better than it already is when it's already locked to a vehicle. It's obviously a personalized bike."

The bike was on loan to him from the Ride2Recovery organization, a group that helps veterans heal with cycling after service.

"This is a lot more than a bicycle I could pick up at the store," Kugler said. "This was given to me by an organization, ridden previously by a Vietnam veteran, a friend of mine, who had given it to me after he was done riding it. It has a lot of nostalgic value to me."

A photo posted by Robert Kugler (@robkugler) on

Kugler explained on social media the bike is not just any bike -- there are only 10 in the world that were ever made.

"It's also likely that you have already understood that you can never ride, nor sell that bike in it's entirety...as it's completely recognizable and there will not be a single bike like it in the entire state of Colorado," Kugler pointed out in a lengthy Facebook post.

His post has been shared nearly 700 times, and Kugler said he's in the process of making fliers for the one-of-a-kind bike.

"I think this is something we can track down because there are only 10 of these mountain bikes," Kugler said. "It's pretty unique, I think we can track it down."