"For the last 100 years or thereabouts, we have been working on a thing called Everyday Life," said the band in the typewritten message.

It will be a double album, split into two halves, called Sunrise and Sunset, and released on 22 November.

The letter was signed by all four members of the band - but the recipient initially thought it was a hoax.

"Fake alert!" said Lena Tayara on Twitter, alongside a picture of the gold-embossed card. "Got this in the post this morning... Can't see why anybody would send it."

After fans reassured her it looked authentic, she changed her mind, writing: "If I'd known that card was genuine I would have put on a nicer tablecloth before I took the pics.

"But thanks for the card - I'm AMAZED and very touched."

'Experimental side'

Coldplay are the biggest-selling British band of the 21st Century. According to the Official Charts Company, they have three of the top 20 best-selling albums of the Millennium, led by 2002's A Rush Of Blood To The Head.

Their last record, A Head Full Of Dreams, was an uplifting, multicoloured dalliance with pop that saw the band collaborate with Beyonce, Stargate and Swedish pop maverick Tove Lo. It sold more than 2 million copies, and spawned 122-date world tour that grossed $523m (£402m) at the box office.

It was followed up by a companion EP, Kaleidoscope, and a side project with Pharrell Williams under the name Los Unidades, but the band have largely been silent since 2017.

Rumours of their return were sparked last week, when black-and-white posters appeared in Madrid, showing the band dressed as a 1920s wedding band, sitting next to a man who appeared to be German philosopher Friedrich Nietzsche, holding a saxophone.

Posters recently appeared in Madrid depicting Coldplay as a turn-of-the-century wedding band

The band's website was later updated to show a logo of the sun and moon, reflecting what we now know to be the album title, while a snippet of orchestral music was posted to their Twitter account over the weekend.

Little else is known about the record but last year, frequent collaborator Mat Whitecross told the NME it would "surprise people", while an unnamed "insider" recently told the Daily Star the album would showcase their "experimental side".

An Italian fan site also posted a proposed tracklist for the first half of the double album, which suggested one of the tracks featured French dance pioneers Daft Punk. However, the information was unverified and potentially fake.

In their letter to Lena, the band simply said the record "is sort of how we feel about things".