US sitcom Gossip Girl's leading lady Blake Lively has planned a belated birthday party to celebrate recently turning 21-years-old.

The celebrity event in New York City is sure to be a haven of photo opportunities of the actress partying it up with her star-studded guest list.

Reports suggest that the birthday girl has decided to mark the milestone with Jazz-themed festivities.

A source told In Touch magazine: "All the guests have to wear 1920s-style clothing. The doormen are checking and will reject those not in theme."

The Hollywood starlet celebrated her actual birthday on August 25th on the set of hit TV show Gossip Girl.

Choosing a 21st birthday gift for the actress proved difficult for co-star Leighton Meester who said: "That girl has everything."

Blake first shot to fame back in 2005, playing the role of Bridget in teen movie The Sisterhood of the Traveling Pants, alongside Ugly Betty star America Ferrera.