Hear'Say and Liberty X will reunite for a 13-date arena tour across the UK and Ireland in 2027.
The Popstars: The Originals tour marks the first time the two groups, both formed through Popstars in 2001, will tour together.
Hear'Say will perform as a four-piece featuring Danny Foster, Kym Marsh, Suzanne Shaw and Noel Sullivan.
Myleene Klass will not take part, according to Official Charts.
Liberty X will return with its original five-member lineup of Michelle Heaton, Jessica Taylor, Kelli Young, Tony Lundon and Kevin Simm.
Tour Dates and Ticket Details
The tour opens April 17, 2027, at 3Arena in Dublin and runs through May 9 at M&S Bank Arena in Liverpool.
Stops include Belfast, Bournemouth, Nottingham, Brighton, Cardiff, Birmingham, Leeds, Newcastle, Glasgow, London and Manchester.
Ticket pre-sale begins at 9 a. m.
Wednesday, October 14, for fans who register for Popstars: The Originals.
Remaining tickets go on general sale Friday, October 16.
Hear'Say described the reunion as a significant milestone after 25 years and said sharing the stage with Liberty X would add to the occasion.
"Coming back together after 25 years is something that's incredibly special to all of us," Hear'Say said.
"It's a chance to celebrate an unforgettable chapter in our lives, reconnect with each other and relive so many amazing memories."
The group also highlighted its return to live performances and its connection with fans from the original Popstars era.
"To be sharing the stage with Liberty X makes this celebration even more special, and it feels like the perfect way to mark such an incredible milestone," Hear'Say said.
Hear'Say said the reunion would combine memories from its early career with new experiences on the 2027 tour.
"We are so excited to be celebrating with everyone and honestly can't wait to reconnect with the Hear'Say fans," the group said.
"To relive those amazing memories together and create some new ones along the way is going to be very special."
The group said anticipation was building ahead of the tour, which will visit 13 arenas across the UK and Ireland.
"We are counting down the days and can't wait to see you there," Hear'Say said.
Liberty X also marked the 25th anniversary of Popstars and its impact on the members who went on to form the group.
"It's hard to believe it's been 25 years since Popstars changed all of our lives," Liberty X said.
"We are thrilled to be heading out on tour with Hear'Say to celebrate where it all began."
According to Official Charts, Hear'Say formed in 2001 from five Popstars finalists and scored two consecutive No. 1 singles with Pure And Simple and The Way To Your Love.
The group's debut album Popstars also reached No. 1 on the Official Albums Chart for two weeks.
Everybody peaked at No. 4 and Lovin' Is Easy reached No. 6, completing four consecutive Top 10 singles.
Liberty X formed from the five Popstars finalists who did not join Hear'Say.
According to Official Charts, Thinking It Over reached No. 5 in 2001 before Just A Little reached No. 1 the following year.
Official Charts records eight UK Top 10 singles for Liberty X, including Got To Have Your Love at No. 2, Being Nobody at No. 3, Song 4 Lovers at No. 5 and A Night To Remember at No. 6.
Its debut album Thinking It Over reached No. 3.
