The Irish singer lost his family home and the majority of his possessions after his property firm went into receivership in 2012 and he later filed for bankruptcy.
Filan admits he was teetering on the edge of disaster when his bandmates decided to separate, and the star feared he would be ruined as he would no longer have an income to pay his mounting bills.
However, he decided against telling his colleagues about his problems, so they had no idea about his struggle when they made the call to quit.
He tells Britain's Daily Mail, "The couple of years before I was declared bankrupt were the roughest. The bank letters, the pressure, the stress was awful. You're in this twilight zone of not knowing where your life is going and yet you're in Westlife.
"Everything was great with the band. I was earning money and it looked good... Then they decided we were finishing as a band. I went out of the room thinking: 'Oh my God, if they only knew.' That was probably the scariest time of my life. My job was finishing, my financial security was ending and I knew I still had the bills coming in every month.
"That's when I realised I needed to get the lawyers involved. It was a scary time, especially when your three little children don't know anything: they just think Daddy's a superstar."
Filan eventually confessed all to his bandmates during their farewell tour. He later had to give up almost all of his belongings, including his house, car and even his wedding ring, to help pay off his debts.