The party will see veteran pop/ska band Madness perform an exclusive concert on the traffic-free central London street.
Tickets for the exclusive gig featuring Madness will be given away free to Absolute Radio listeners via an on air text message competition.
The Regent Street Festival will offer "exciting events, activities and in store offers for all the family throughout the day" and will be followed by a rock ‘n' roll birthday bash hosted by the radio station's Breakfast Show DJs Christian O'Connell and Geoff Lloyd.
Outside Hamleys there will be a children's lawn, which will be home to face painters, animal characters, a birthday tea party, balloon artists and magicians.
In addition there will be a fashion show, stilt walkers, roaming musicians, a ferris wheel, and a carousel.
In Regent Street food quarters Heddon Street and Swallow Street the restaurants will adopt the birthday theme with special parties, kid's menus and cocktails.
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