It’s fitting that when it came time for Mo Johnston’s twin boys to pick soccer teams to support, one chose Celtic, the other opted for Rangers.

“I never brought that on whatsoever,” the Toronto FC general manager said with a laugh.

“They’ve been back to Scotland without me,” he said of nine-year-olds TJ and Tyler. “The grandparents have told them all about me.

“They came back with Rangers and Celtic tops.”

Twenty years ago this summer, Johnston stunned Scottish soccer fans by signing with Rangers, the arch-rival of cross-town Celtic, the club he supported as a boy growing up in Glasgow and starred with from 1984-87.

Coming off two seasons in France, the Scottish international striker just weeks earlier was poised to return to Celtic, identified as the Catholic team in a century-old rivalry where sport blurs with religion and sectarian violence.

But in July 1989, Johnston, then 26, was unveiled to a disbelieving media and public as the newest member of the Rangers.

The move, considered to this day the biggest in the history of Scottish soccer, outraged some supporters on both sides of one of the most intense rivalries in sports.

Celtic fans, who had adoringly called Johnston MoJo, now labelled him Judas. On the Rangers side, some people tore up season’s tickets and burned scarves after their predominantly-Protestant club signed a high-profile Catholic.

Death threats and a 24-hour security detail followed.

But this week, as Celtic FC arrived to take on Portuguese giant Benfica in a friendly at BMO Field tonight, Johnston, who rarely talks publicly about this chapter in his life, reflected on “living the dream” of playing for both legendary teams, collectively labelled the Old Firm.

“There are many happy moments on both occasions,” Johnston said of winning league championships and being named player of the year with each team. “It’s special being part of an organization that’s synonymous with world soccer.

While Johnston wasn’t the first Catholic to sign with Rangers, he was the most high profile at a time when the club was publicly trying to overcome its sectarian reputation by signing players without taking account their religion.

He’s quick to answer when asked if he’d make the move knowing all that was in store for him.

“Absolutely. I felt it had to be done. I felt the barriers had to be broken,” he said. “And, to be honest with you, it was difficult at first, but when teammates and fans start to embrace you then it becomes a lot easier.”

Celtic vs. Benfica

• Celtic FC takes on Portugal’s Benfica tonight in an international friendly at BMO Field.

• Celtic are off to a strong start in the Scottish Premiership, winning their first three games of the season.

• Benfica sits third in Portugal’s Liga, having won two of three to start the season.