Mariah Carey's low-key anniversary
The couple shut down Disneyland and donned Princess and Prince Charming gear to renew their vows for their fifth anniversary last year.
But according to Nick, they opted for a low-key affair when they celebrated their sixth anniversary - which falls on the same day as their twins' birthdays - in April.
The America's Got Talent host told Parade: "We definitely had a good time. The first part of the day, we threw a birthday for them (the twins) and their friends at their school, and then after that, once we tired all the kids out, we had a nice romantic rooftop evening and kind of re-enacted some of our wedding and engagement rituals that we do every year.
"So it was low key. I mean the year before, we kind of went over the top with Disneyland, so we kind of wanted to reel it in this year so everybody doesn't think that we try to do that every single year."
Nick also dismissed the rumours that his marriage is in trouble.
"You kind of have to ignore it because every week it's something different, and if you paid attention to it, it actually probably would start really affecting you... There's no merit or truth to it. It's kind of humorous, really. It couldn't be further off from the truth," he told the magazine.