Brian, 35, and wife Leighanne, 41, who have a seven-year-old son - Baylee - together, recently renewed their wedding vows after 10 years of marriage.
Asked why they picked that date, Brian said to OK! magazine: 'It's funny. We were trying to do it the weekend before, but the Backstreet Boys were wrapping up our Canadian and US leg of the tour - of the This is Us tour.
'We wanted to have more time to prepare when we got home. It ended up falling on September 11, and what it signified about September 11 is not only were we celebrating our vows and renewing each other, but we were also celebrating life.'