Katy Perry's romance with John Mayer is back on. The on-again/off-again couple were spotted celebrating John's 35th birthday in New York together yesterday less than a week after the 'Part Of Me' singer dumped the 'Half My Heart' singer telling him to lose her number. They enjoyed a romantic lunch together at New York's trendy ABC Kitchen to celebrate John's special day. The couple - who first started dating in June - were also seen having dinner at Pearl restaurant in the city before going clubbing together on Sunday night. Katy - who will celebrate her 28th birthday on October 25 - is preparing to host a divorce party later this month on what would have been her second wedding anniversary with Russell Brand on October 23. A source said: "Katy has been dreading October 23 for weeks now and has been trying to think of ways to turn it into something positive."