R&B queen Beyonce has quietly released a love song dedicated to her husband, hip hop mogul Jay Z, available only on his new streaming service Tidal.

Songstress Queen Bey posted a 15-second preview of the acoustic ballad "Die With You" on her Facebook page Saturday in celebration of the couple's seven-year wedding anniversary.

"I don't have a reason to be if I can't be with you," Beyonce sings softly as she plays the piano, wearing a backwards cap, blond pigtails and appearing make-up free.

"'Cause Darling I wake up just to sleep with you / I open my eyes so I can see with you / and I live so I can die with you," she sings in the home-video style clip.

The camera moves around her as she croons, eventually turning on the filmer: the lucky man himself, husband Jay Z.

The rebranded Tidal streaming service was launched in March by Jay Z, backed by major music heavyweights including Madonna, Kanye West and the masked electronic duo Daft Punk, who will all be equity partners in the new Tidal and offer exclusive content.

The site also features exclusive music videos from R&B singers Rihanna and Alicia Keys and rockers The White Stripes.

Jay Z bought Tidal earlier this year for $56 million from its Swedish-listed parent company Aspiro and markets itself to audiophiles.

In a promotional video released after its launch, the company said it is focused valuing artists for their talent, and not treating them as mere products, in a stab at other unnamed streaming companies.

Beyonce posted the song unexpectedly on social media, much like the surprise release of her eponymous album last year that quickly became a top-seller around the world.

By Sunday afternoon, Beyonce's "Die With You" Facebook post had been shared close to 10,000 times and "Liked" by 129,000 fans.