Stade Francais and Racing 92 have sensationally announced they are to merge ahead of the 2017-18 campaign.
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.
Monday's announcement stunned the rugby world, with the two clubs releasing identical statements to confirm their plans.
"These two flagship clubs of Paris and the Hauts de Seine, beyond the sporting rivalry they have enjoyed, have many other similarities: a strong local and regional anchorage, a historic educational mission, ancestral ties with the Olympic movement and an inextinguishable will to progress in all areas," the statement read.
"It is on the basis of these principles that the two clubs lay the foundations for a merger project by pooling their resources to better cope with the challenges of performance and education.
"This association, effective from next season, must give birth to a new club that will preserve the roots of Racing 92 as those of Stade Francais Paris, while multiplying the means put at the service of youth and French rugby.
"Consolidated by its dual culture, by the fierce determination of its two presidents and its increased audience in a population pool unmatched in France, this new club has a long-term commitment to build a true reference day after day."
The two clubs are a long way from repeating their respective title-winning feats of the past two years this season - Racing mired in mid-table, while Stade lie 12th.