After the minister tells him that Sirius Black is loose and Harry finds out that he is the most likely target, he runs off as soon as he can get some of his gold from Gringotts.
In France, he runs into a stunning woman who is quite concerned that a 13 year old is running around who does not even speak French. She takes him to her house for the night and, the next morning, tries to figure out what to do with Harry. After a long talk with him, she calls her cousin, who has a daughter roughly Harry's age while she deals with the international angle.
As it turns out, Harry ended up running into the Duchess of magical Lorraine, an independent Veela state through a quirk in Habsburg inheritance shortly after the SoS. And the cousin turns out to be Appoline, her daughter Fleur. At first, communication is difficult, Harry picks up a bit of French, Fleur speaks broken English, but they make it work and become good friends.
It is decided that Harry will have to return to Hogwarts, which will receive extra protection since his conclusion about Sirius Black is most likely right. So at the end of summer, there is a tearful goodbye and they promise each other to exchange letters. At the end of the year, Sirius is quietly whiskered away to Lorraine and Harry and Fleur get to spend another summer together.
So when Beauxbaton shows up for the triwizard tournament, the Hogwarts students are quite surprised when Harry greets the "hot Veela chick" like an old friend, and the platonic kisses on his cheek result in three duel challenges for Fleur's hand. They spend the entire next day together, so when Harry's name comes out of the Goblet, Fleur knows that Harry didn’t put his name in because she had been with him the whole time. And when Moody points out the "accident" angle, she starts making plans about preparing together with Harry, everything else be damned.