The Jonas Brothers smile up a storm while celebrating the launch of their new book, “Burning Up: On Tour with the Jonas Brothers” at the Sunset Tower Hotel in Los Angeles on Monday.

The musical trio — Nick, Joe and Kevin — performed their song “Shelf” on The Tonight Show with Jay Leno and sat down to talk with the host for a quick minute. Nick, the youngest of the trio at 16, explained the hilarity behind Kevin’s constant reminder about his birthday. He shared, “Here’s the thing. Kevin always makes a point to say, ‘You know, I hope you guys don’t forget it’s my birthday on this day because last year you forgot.”

Kevin goes on to explain that he does it on purpose. He said: “It was six o’clock on my 18th birthday when they finally realized that ‘Oh yea, it’s Kevin’s 18th birthday’.”

Check out their performance below and check out the rest of their interview too!