Lady Gaga joins pal Tony Bennett at 90th birthday bash

Lady Gaga helped pal Tony Bennett ring in his 90s on Wednesday (03Aug16).

The pop star joined her jazz standards collaborator as he lit up the Empire State Building in New York City to mark his milestone age.

Newly-single Gaga, who split from actor fiance Taylor Kinney last month (Jul16), wore a black gown and a wide-brimmed black hat for the birthday surprise.

Bennett is hoping to reunite in the studio with the Poker Face star next year (17) for a follow-up to their hit collection of jazz duets, Cheek to Cheek.

"She's so busy right now, but at the beginning of next year we'll start doing an album," he told Billboard. "The first one went way over a million, and it's still selling."

The album landed the odd couple a Grammy Award for Best Traditional Pop Vocal Album in 2015.

Bennett will open up about his famous friendships with the likes of Gaga, Amy Winehouse and Frank Sinatra in a new memoir, titled Just Getting Started.

"The whole book is about different performers and just my experience about meeting them and the different things that happened and why they were so popular internationally throughout the world," Bennett told Billboard. "They're all people who were completely committed to doing great shows and great things, and they were all different, each of them."