Neil Patrick Harris on the Key to a Successful Marriage: You Need to Talk It Out

The actor spoke to ET after his one-year wedding anniversary.

Neil Patrick Harris and husband David Burtka celebrated their one-year wedding anniversary this month during a summer when many celeb couples are going their separate ways. ET caught up with NPH and got him to open up about his key to a happy marriage.

"You got to ebb and flow," Harris said. "The relationship changes. The definition of it changes."

PIC: Neil Patrick Harris Celebrates One-Year Anniversary to David Burtka

Harris, 42, wed Burtka, 40, after 10 years of dating and the two are the proud parents of 4-year-old twins Gideon Scott and Harper Grace. The Emmy-winning actor admitted that having children transforms a relationship and insisted that managing your own expectations can help you be more flexible when it comes to adapting to changes in a relationship.

"If you are too rigid about what your expectations are and then suddenly it changes, then you have more reason to want to look elsewhere for stuff," Harris noted. "In our relationship, communication is super important. Good friends of ours said, 'You need to talk it out,' and if that means raising your voice, you need to raise your voice. Know what you're talking about. Know where you're standing as opposed to letting stuff build up, I guess."

WATCH: Neil Patrick Harris Pranked 'The Voice' Coaches and It Was a Truly Terrifying Experience for Him

Harris spoke to ET while promoting his new hosting gig for NBC's variety show, Best Time Ever. On the show, which boasts that anything can happen, one of the host's tasks is to prank celebrities -- a feat he admitted can be scary. Harris described one such prank where he tried to get the best of The Voice coaches.

"I was Jurgen Vulmer, who was the host of The Voice Austria, which doesn't exist," he said, explaining the prank, which consisted of asking the coaches a bunch of random, strange questions. "I had almost three hours of prosthetic makeup on. I looked nothing like
myself, and had a different accent."

WATCH: Neil Patrick Harris on His Much, Much Younger Celebrity Crush, Nick Jonas

"It was incredibly terrifying," he continued. "They thought I was insane."

Best Time Ever airs Tuesdays at 10 p.m. ET/PT on NBC.