British pop star Jessie J is to play a free show in London on Thursday (27Mar14) to celebrate her birthday. The Price Tag singer announced the acoustic gig at the Oslo Hackney venue in east London just hours before showtime, and urged fans to turn up early as entry is on a 'first-come-first-served' basis. Jessie J, who turns 26 on Thursday, branded the event a birthday surprise, writing in a post on Twitter.com, "I'm performing a special acoustic set (at) Oslo Hackney Tonight at 7pm - first come first serve (sic). Free entry! 18+ only. Birthday behaviour." The singer later thanked fans for their birthday wishes, adding, "Too many messages to reply to them all! Thank you for your kind wishes and love! I will enjoy every bit of today! Promise."