|Singers Matt Goss (left) and Luke Goss, formerly of Bros, pose for a photocall in London on October 5, 2016|
The 48-year-olds, who garnered a huge teenage fanbase with hits such as "When Will I Be Famous?", will play London's 20,000-capacity O2 Arena on August 19.
"Last year, I can honestly say I didn't think it was going to happen. I thought the moment had genuinely passed," lead singer Matt told a surprise press conference in London.
"I met Luke one day for a beer and said: 'it's time'."
With Luke on drums, Bros burst onto the pop scene in 1987 with their single "When Will I Be Famous?", which hit number two in the British charts.
Follow-up single "Drop The Boy" did likewise, while "I Owe You Nothing" reached number one in 1988.
They last performed together before 77,000 fans at London's Wembley Stadium on August 19, 1989, before going their separate ways in 1992 after their third album.
The brothers are now based in the United States. Matt continued as a solo singer and has enjoyed a seven-year residency at Caesar's Palace in Las Vegas.
Luke is a Hollywood actor, appearing in "Blade II" (2002), "Tekken" (2010) and "Interview with a Hitman" (2012).
"I've got to learn to play drums at a level that I'm happy with again. I can't wait to go through the pain and the blisters," he said.
"By the time we get there, we'll be so prepared."
He said the band would play their familiar songs in a contemporary way, rather than introduce new material.
"It is a 2017 show," he said.
Matt added: "Nothing has ever compared to having my brother on stage with me.
"We're perfectionists. We both want it to be a spectacle. This is going to be the best show that Bros has ever done."
Tickets go on general sale on Friday.