The former Westlife star, 32, tied the knot with model Vogue Williams, 26, last week. Speaking to Hello magazine, he admitted he "had no idea what he was doing" when he married his first wife Kerry in 2002.
"This is me getting married for the rest of my life and a completely different life," Brian said of his new relationship.
"I was 18 or 19 when I got married the first time. I was in Westlife. I had no idea what I was doing. It wasn't till I was 30 that I turned into an adult."
Brian was actually 22 when he married former Atomic Kitten star Kerry five months after the birth of their first daughter Molly, now 11. The couple had another daughter, Lily, now nine, before splitting in 2004.
Brian's comments have enraged his ex-wife Kerry, who took to Twitter to vent.
"I will never let anyone take away my first marriage not even my ex-husband!" she wrote.
"We may have been young but I knew full well what I was doing!!! And never in a million years would I ever dismiss it, especially bringing two amazing children into it... Love mummy xxx."
She added, "Just want my children to know there were made with love and no regrets #eyeswideopen."
And one more point: "Just want to say a big thank you to all the people who have walked in and OUT of my life You've all made me the person I am today.... Stronger, wiser and one hell of a great mum!! Thanks xxxx."
Kerry has two other children with her second husband, taxi driver Mark Croft, who she split from in 2011.