The Skyfall songstress took to Twitter on Sunday, the eve of her 26th birthday, to write: "Bye bye 25... See you again later in the year x".
The cryptic message will have her fans on tenterhooks as they wait for the release of her third album – the star's two studio album titles to date have been named after her age at the time they were written.
Her first record, called 19, was released in January 2008 when she was 19 years old, and her second was titled 21, which came out in January 2011 when she was 22.
In the snap accompanying the message, the Birthday Girl is make-up free and fresh-faced, snuggled up on what appears to be the sofa at home.
The notoriously private star, who won an Oscar in the Best Original Song category for her 007 theme tune Skyfall, has kept a low profile since the arrival of her son Angelo back in 2012.
Since then she has been enjoying time out with her little boy, now 18 months, with partner Simon Konecki, making just a few appearances at global events including the Academy Awards and the Golden Globes.
Then in December last year, Adele made a rare public appearance to receive an MBE for her services to the music industry.
The singer was given the honour by Prince Charles during an investiture service at Buckingham Palace.
She said later: "It was an honour to be recognised and a very proud moment to be awarded alongside such wonderful and inspirational people. Very posh indeed."