When fans saw J-pop boy band Arashi during their press stop at Jewel Changi Airport on Sunday, it was the last time they saw member Kazunari Ninomiya as a single man.

The 36-year-old announced on Tuesday night, a day following the group's return to Japan after a whirlwind Asia press conference tour, that he had tied the knot on Monday to "a woman (he has) been dating for a while".

While he did not name her, Japanese media reported that she is Ayako Ito, a 38-year-old former television presenter who retired from the limelight last year.

Ninomiya and Ito have reportedly been romantically linked since 2014 after filming a television show together.

In a handwritten letter posted on the Arashi fanclub site, Ninomiya announced, writing: "I have spent more than half my life as a member of Arashi, but now I am making a decision as a man."

He added: "I'm sure many are shocked by this sudden news, but to ensure that my decision will be looked upon favourably in the future, I will do my best as Kazunari Ninomiya from now and beyond. If I could have your support, I will be most delighted."

The baby-faced Ninomiya is the first of Arashi's five members to get married. The group is under the boy band agency Johnny & Associates, which is notorious for barring its talents from dating publicly.

News of his marriage trended worldwide on Twitter on Tuesday night and yesterday morning.

The other members of Arashi, which recently celebrated their 20th anniversary, wished Ninomiya well. Sho Sakurai, 38, told the Japanese media: "He is a childhood friend I have known since middle school and I wish him happiness."

Another band member, Masaki Aiba, 36, says: "We have been friends for 24 years. We used to take the train to and from work as middle-schoolers. He is my comrade and a beloved friend. This is the path my friend has chosen. I wish Kazunari Ninomiya happiness. Congratulations."

Arashi are slated to suspend all their group activities to go on an indefinite hiatus at the end of next year.