Former Racing 92 scrum-half Mike Phillips has been stunned by the impending merger of the club with local rivals Stade Francais, claiming squad members from the two sides were even discouraged from living near each other during his time in Paris.
Phillips, 34, spent three years at Racing from 2013 until last year, when he moved to Premiership side Sale Sharks.
The ex-Wales and British and Irish Lions number nine is not alone in being taken aback by news of the merger, which was revealed jointly by the clubs on Monday.
"It's a huge shock, there's a big rivalry in the derby games," Phillips told BBC Sport.
"I'm massively surprised.
"The guys [at Sale] talked about it in training and firstly I said 'That's not true, it's just the French media' but it was for real.
"Stade won the league two years ago, they beat us two or three times, then the following year we managed to win the league and our president Jacky Lorenzetti was thrilled.
"Both clubs have got a huge history in French rugby and Stade Francais have won the title many times, they have a massive tradition just like Racing.
"You weren't allowed to live in a certain area because that's where the majority of Stade Francais players lived and that was pushed by Jacky Lorenzetti, he was in control of that."
Stade players Pascal Pape and Paul Gabrillagues have both expressed their dismay at the merger, but Lorenzetti has insisted the outcome will be beneficial.
"You can see things positively instead of saying 'one club is disappearing', no. It will be an amazing club," he told a news conference.
"If we don't make any mistakes, it will be an amazing club and we strongly believe in it with [Stade president] Thomas Savare."
The two giants of French rugby have 20 domestic titles between them, including the first two in 1892 and 1893, as well as the two most recent crowns - Stade prevailing in 2015 before Racing defeated Toulon in the final last year.