'Rottweiler' Valerie bares her teeth as she steals the limelight from her rivals

Francois Hollande moves into the Elysee Palace this Thursday, but he is already facing a very domestic crisis. Ever since he was declared France's 24th president a week ago, his lover, the elegant Paris Match journalist, Valerie Trierweiler, 47, has been making headlines of her own.

For instance, Le Canard enchaine, France's answer to Private Eye, published an angry text message from Trierweiler to Mariana Grepinet, a colleague.

Grepinet had mentioned, in what would otherwise be described as a puff piece about France's new presidential couple, one of Hollande's children with Segolene Royal, the 2007 Socialist presidential candidate and Hollande's former lover of 23 years.

The article did not explicitly state that the couple were no longer together. "What game are you playing?" the text threateningly ended.

Then there was Olivier Bourg, the radio presenter and stand-up comic, who tried to pull his trademark trick of calling Trierweiler's mobile to wheedle careless statements from her, as he had from countless celebrities before. Trierweiler sussed him out fast enough, and retorted on air, in a pinched voice, "I won't forget this", before hanging up.

In case anyone hadn't got the message, on Wednesday, Trierweiler, who Nicolas Sarkozy once referred to as "Rottweiler", blocked Julien Dray, an MP and one of Hollande's key campaign managers, from setting foot inside the victory party.

His offence appears to have been to invite Dominique Strauss-Kahn, the former International Monetary Fund chief, to his birthday event days earlier. Strauss-Kahn, Hollande's rival for the Socialist presidential nomination until a New York hotel maid complained of sexual assault, mingled with Hollande's closest advisers. Even worse, the party was held in a fashionable new restaurant in a refurbished sex shop in Paris's red light district.

Any doubt over the political jeopardy this entailed was dispelled when Sarkozy brought up Strauss-Kahn's attendance, to lambast Hollande during their heated television debate three days before the final vote.

But party insiders suggest Trierweiler has "had it in for Dray" for far longer. Since 2007, in fact, when he was Royal's election campaign manager. "Valerie", they will tell you feelingly, "can certainly bear a grudge".

This had been known in political circles for a long time, but is emerging only now that media attention has turned to France's new premiere dame.

When Trierweiler, a twice-divorced history graduate who has spent almost her entire career at the celebrity-obsessed Paris Match, told an interviewer she would not be a "potiche" (a decorative nonentity), it was widely interpreted as a swipe at her predecessor, Carla Bruni.

Asked how she would cope with life in the front line of French politics, she said, patronisingly, that she was far better equipped than Bruni for the role: "She came from a world totally alien to that of politics. She did not necessarily know the political codes."

This is not only dismissive but ill-judged. During her four years in the Elysee, Bruni did not put a foot wrong. She is cultured and has excellent manners. She has a sense of humour and even made friends with the journalists who lampooned her. When Le Canard enchaine ran a spoof column, Carla B's Diary, Bruni laughed about it among her friends and invited its author to the Elysee.

Trierweiler, by contrast, has already alienated people she ought to have been assiduously cultivating; and much of that stems from her involvement with Hollande and antagonism with Royal.

Trierweiler first met Hollande in 1988, when she was a bright, 23-year-old reporter and he was a 34-year-old MP, a former Mitterrand aide and part of the new intake.

In 1992, Trierweiler covered the birth of Flora, Royal and Hollande's fourth child.

Meanwhile, Trierweiler had three boys during her marriage to Paris Match sub-editor, Denis Trierweiler.

In 2005 she began her affair with Hollande, who was still living with Royal and their four children. When news of it reached Alain Genestar, the then editor of Paris Match, she refused to see any potential conflict of interest between her private life and her job covering the Socialist Party for the magazine. Eventually, Genestar told two journalists, he had to shift her to the cultural section of the magazine. Trierweiler, who loves the political scene, was said to be resentful.

By 2007 Royal had beaten Hollande to become the Socialist Party's presidential candidate. Despite his affair with Trierweiler, he campaigned alongside Royal as her lover, but appeared resentful and unconvincing.

Trierweiler was blamed by some for encouraging Hollande's passive-aggressive stance towards Royal's candidacy. Royal would send Hollande her speeches in advance; he'd then call her minutes before she stepped on to the dais to say that the speech was all wrong. The night Royal lost to Sarkozy, the fiction that she and Hollande were together was dropped with a very public press release from Royal.

But Trierweiler's hostility towards Royal appeared to persist. One insider recalls the time that Hollande answered a question about Royal during a television interview in 2010, then received an angry text message from Trierweiler. As Franz-Olivier Giesbert, his interviewer, tried to reassure him that he had not strayed from politics in his reply, he said: "You don't realise, I'm going to get hell at home."

In January, Hollande's first major campaign speech as Socialist presidential candidate was introduced by a video tracing the past 40 years of the party. Jarringly, to many of the rank and file, it ended in 2002, the year that Lionel Jospin came third in the first round of the election, leaving the party without a candidate in the final run-off. Royal's 2007 presidential bid was omitted, a decision that was chalked up to Trierweiler's influence.

Despite loyally supporting Hollande as he fought for the party's nomination, Royal was relegated at the campaign launch to a distant seat, while Trierweiler stood close to her lover. Aides said Royal collapsed in tears afterwards.

Trierweiler had her own office at Hollande HQ during the campaign, but her feminist-sounding line is that she remains a journalist and, in any case, needs the work to support her own family. Friends say she's writing the text for an instant coffee-table photo book on the campaign, to be published next month.

Yet Royal is not about to slink quietly from the Socialist scene. She is aiming for a role as Speaker of the National Assembly, keeping her at the forefront of French political life.

Trierweiler's career is now under the spotlight. When the political talk show she hosted on a cable television station was cancelled, Paris Match offered to pay her to, in effect, stay at home. She is resisting that plan angrily. In an interview with tomorrow's Elle magazine, she says she would rather interview "foreign personalities" to keep "a proper distance" without "impeding Francois Hollande's work".

But she will never be far away. On election night at the Place de la Bastille, it was she who ordered Hollande, whose style this definitely is not, to kiss her on the mouth, thus securing the perfect picture.

Trierweiler will make her international debut at next weekend's G8 summit at Camp David in the US. At the time of writing, there is wild speculation that the president and his love might hastily get married this week. And live happily ever after, of course.