LONDON (AFP) - British pop-rock giants Coldplay announced Friday that their seventh album, A Head Full Of Dreams, will be released on Dec 4, having hinted it may be their last.

Fans were atwitter on social media on Tuesday when cryptic artwork was released online, matching a mysterious London Underground poster that led to speculation a new album was in the pipeline.

The band confirmed the gossip on Friday, and premiered the album's upbeat first single Adventure Of A Lifetime on BBC radio, suggesting a departure from last year's subdued album Ghost Stories.

Singer Chris Martin previously described the record as "the completion of something", sparking rumours it could be their last.

The album, produced by the team behind Katy Perry's Firework and Beyonce's Irreplaceable, will feature a raft of guests including Beyonce and Oasis star Noel Gallagher.

Eagle-eyed fans were alerted when a pattern that Martin had worn on a T-shirt at an event in Global Citizen Festival in New York in September appeared on social media earlier this week.

The interlacing rainbow-coloured rings on a black background had appeared on a poster in the British capital's underground train network with text reading only "December 4".

On Monday and Tuesday, the band - responsible for hits such as Yellow, Viva La Vida and Clocks - released two animations of the colourful pattern on its official Twitter and Facebook pages.

In all, the band has sold over 100 million albums worldwide and won numerous accolades, including seven Grammy Awards, multiple MTV awards and eight Brit Awards.