Chris Martin, Coldplay

Chris Martin of Coldplay performs as part of the iTunes Festival at the Moody Theater on March 11, 2014 in Austin, Texas.

Tim Mosenfelder/Getty Images

Coldplay fans have solved a mystery that has posters across London spelling out the release date of the band's new album. 

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Black posters with a rainbow-colored geometric Flower of Life shape on them and the date "December 4" printed at the bottom had been appearing around the city. Some astute fans noticed that shape was the same as one printed on frontman Chris Martin's T-shirt at the Global Citizen Festival in New York last month, jumping to the conclusion the two are related. 

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A source tells Billboard that a new Coldplay album will be out by the end of the year, but did not confirm the posters' connection. An announcement is expected imminently. 

Last winter, Martins revealed that the band was at work on their seventh studio album and that it was likely to be its last

"It's our seventh thing, and the way we look at it, it's like the last Harry Potter book or something like that," Martin said then. "Not to say that there might not be another thing one day, but this is the completion of something."

He added, "I have to think of it as the final thing we're doing. Otherwise we wouldn't put everything into it."