London Mayor Boris Johnson is giving Prince William and his new bride, Kate Middleton, a Bixi tandem bicycle for their wedding.

The regal tandem was designed specifically for the royal couple, drawing on the rental bicycle model created in Quebec.

Johnson, an outspoken advocate of urban cycling, is offering the bicycle as a gift from the city of London.

He posted a cartoon on his office's official YouTube channel, showing the royal couple riding their new tandem.

The royal seven-speed two-seater was designed by Michel Dallaire, who created the original Bixi bike.

Cycle Devinci Inc. in Chicoutimi, Que. manufactured the tandem after receiving the secret order two months ago.

"It's a cool project," said Bixi Montreal spokesman Michel Philibert. "Just to see our Bixi at the royal festivities, I think we have to be honoured by that."

London's gift speaks to the bicycle's growing popularity around the world, said Roger Plamondon, CEO of the Public Bike System Company, which oversees the rental bike system.

The tandem, built in Chicoutimi, has seven speeds and two bells. (Public Bike System Company)Plans are underway to build more two-seater Bixis for promotional purposes, but "we're not sure if we will offer them at Bixi stations" because they're too long, Plamondon said.

The Bixi bike was first introduced in Montreal in 2008.

Several major cities around the world have since adopted it, including London, Melbourne, Minneapolis, Washington DC and Ottawa.