François Hollande's partner takes Twitter swipe at his ex

Valérie Trierweiler (L) took a swipe at Ségolène Royal, with a good luck tweet to the dissident Socialist candidate standing against Royal in parliamentary elections. Photograph: Patrick Kovarik/AFP/Getty Images

François Hollande's partner, Valérie Trierweiler, has sparked a political storm and embarrassed the Socialist party by tweeting her support for a dissident candidate standing against Hollande's ex-partner, Ségolène Royal, in the parliamentary elections.

The saga threatens to damage Hollande, who has been careful to style himself as a down-to-earth "president normal" but now faces charges from the right that animosity between his present and past girlfriends has turned his leadership of France into a celebrity soap opera worthy of the worst excesses of Nicolas Sarkozy's highly public love life.

Trierweiler's unexpected tweet comes at a critical time for the Socialists. Royal, who is the mother of Hollande's four children and was his long-term partner before he moved in with Trierweiler in 2007, is facing a difficult fight for a parliamentary seat in La Rochelle.

She topped the poll in the first round but another local Socialist, Olivier Falorni, who came second, has refused to stand aside and is fighting on a dissident ticket in the final runoff this weekend.

The Socialist party, which backs Royal, had pressured Falorni to quit the race.

Hollande was quoted saying Royal was "the only candidate" with presidential support in Royal's latest campaign leaflet, issued on Tuesday morning as the Socialist party leader, Martine Aubry, arrived in La Rochelle to support her.

But just before noon, Trierweiler, or @valtrier – who was once dubbed "Tweetweiler" for her use of the social network – tweeted: "Good luck to Olivier Falorni who has proved himself worthy, who has fought alongside the people of La Rochelle for so many years with selfless commitment."

Paris political circles were so shocked at the tweet, which appeared to be a clear jibe at Royal and a shot in the foot of Hollande, that most thought Trierweiler's account had been hacked. But 40 minutes later, Trierweiler replied to Agence France Presse with a one-word text message that "yes", she had sent the tweet.

An unnamed but dumfounded Elysée adviser who was in an interview with Le Monde at the time, muttered that he'd been prepared for government crises but not "marital" ones.

The saga, which immediately dominated all news media, seemed to play into every stereotype and criticism that Trierweiler had been seeking to avoid, namely that she interfered in politics.

The first lady, a political journalist who once covered the Socialist party, has insisted on continuing her journalistic career and maintains a column on culture in Paris Match. Asked recently on radio if she meddled in politics, she said that charge was totally false.

The French right, in the middle of a fierce parliamentary election campaign in which Hollande hopes to win a Socialist absolute majority, leapt on the tweet.

Geoffroy Didier of the UMP, said Trierweiler's personal "score-settling" meant Hollande's promised "exemplary republic" had turned into a bad "celebrity" saga. "The 'normal presidency' is definitively dead," he declared. "From now on, it's Dallas at the Elysée."

Several rightwing politicians accused Hollande of carrying out a love-life "vaudeville". One warned of "score-settling at the OK Corral". Royal declined to comment. The Socialist leader, Aubry, said the "only thing that matters" was Hollande's support for Royal. The Socialist Jean-Louis Bianco said Danielle Mitterrand, wife of the last Socialist president François Mitterrand, would never have allowed herself to "meddle" in politics.

Hollande is doubly vulnerable as he had vowed that his presidency would be above party politics. Earlier this year, Trierweiler told a magazine: "François trusts me totally except for my tweets." She said she had a strong personality and refused to quit social networking.

The tension between Trierweiler and Royal, who ran for the presidency in 2007 as her relationship with Hollande was ending, has been widely covered in the French media, including Trierweiler's assertion in a recent book about her that she didn't vote for Royal in 2007.

Royal was reported to have been outraged when Trierweiler approached her without warning for a public handshake for the cameras at a rally during the campaign.

On stage at La Bastille after his election victory, footage showed that after Hollande gave Royal a kiss on the cheek, Trierweiler demanded of him: "Kiss me on the mouth."

Royal had backed Hollande during the presidential campaign and had been hoping to win the La Rochelle seat in order to be made speaker of parliament as a reward for her loyalty.

Falorni, who is continuing his campaign battle against Royal, said he was very touched by Trierweiler's message of "personal friendship".