A 145-year-old stamp has Canadian collectors baffled over its existence.

Considered Canada’s rarest stamp, only two known copies of the two cent “large Queen on laid paper” were known until an American stamp hobbyist revealed the discovery of the third copy of the 1870 dated stamp earlier this year. It is believed to be worth $1 million, the Windsor Star reports.

"They started issuing the two-cent-large-Queen in 1868," Grant Duff, a stamp enthusiast told the Canadian Press. "If it was dated 1870, might it have been a fake? It was too good to be true, basically, but they've determined it was a genuine example."

The notion that another copy of the rare stamp existed, prompted a Toronto-based postal history research company to conduct tests on the stamp to ensure its authenticity. In a 10-page report published last month, experts concluded the stamp was real.

"A two-cent large queen was submitted to the expert committee in March 2013 showing laid lines in the paper," stated the July 16 report, prepared by technical specialists from the Vincent Graves Greene Philatelic Research Foundation. "It was not an obvious fake. Accordingly considerable analysis has been undertaken to determine if it is genuine."

The American stamp collector that had the rare stamp bought it for just $5 when he spotted it at a local collector club’s catalog. News of the stamps’ existence was first reported by Canadian Stamp News back in June.

"The first story I wrote -- strange enough for a stamp magazine -- was one where I used anonymous sources," Canadian Stamp News editor Bret Evans told Postmedia News. "It's very rare that you sleuth out a stamp story," he said.

The stamp is so rare because of the profile of Queen Victoria was printed on “laid” paper -- which is commonly used for stationary not stamps. It also has alternating light and dark lines and that points to a time when printers were transitioning to “wove” paper, the Canadian Press reports.

Duff estimates there were 100 to 400 of the stamps printed on “laid” paper. The two that were known to exist were sold for $90,000 and $200,000.

The latest one to be unearthed could be worth $250,000, according to the Unitrade Canadian Stamp Catalogue. But collector and businessman Ron Brigham, who owns one of the rare stamps, said it was valued at $1 million.

"It's possible because it's so rare," Grant Duff said. "Even a third one being discovered probably doesn't hurt the market."