Britain kicked off three days of celebrations on Friday to mark Queen Elizabeth II’s official 90th birthday with a national thanksgiving service in St. Paul’s Cathedral The queen’s milestone birthday is being marked with a three-day series of festivities that will include solemn religious events and street parties in many towns and cities The Queen was actually born on April 21 but in keeping with a tradition that dates back to the 1700s her 'official' birthday is usually celebrated on the second Saturday in June, which this year coincides with her husband Prince Philip's 95th birthday