However, the Orléans are an exception: despite having reigned for only 18 years (deposed amidst the political revolutions that swept Europe in 1848), and having been served by only one king who had a questionable claim on the throne (the old, meaning French, Légitimist line of the Bourbons was still living, as of the accession in 1830 of Louis-Philippe), meaning that they never managed to become a real dynasty, they have nonetheless retained their prestige as a royal house.

Of course, they are of royal origins (since the house is an offshoot of the Bourbons). Still, they could have become relegated to the status of an historical footnote, given how events unfolded. Instead, they've done a remarkable job of maintaining their traditions and remaining active on the royal scene -- contracting impressive dynastic marriages with both reigning and non-reigning houses.

Just look Princess Hélène (1871-1951): despite being a daughter of only a pretender, she was in serious contention for becoming the bride of the Duke of Clarence (Prince Eddy, born second and direct in line to the British throne). As it was, religion got in the way, as it did in the prospective match between her and the Russian czarevich (the future Czar Nicholas II). After all, her older sister became the queen of Portugal.

Members of the house seem to have always had great pride in their heritage, taking part in historical events at every opportunity. The most recent one coming to mind is the formal public apology issued by the current head of the house for his ancestor's actions, and hence partial responsibility, for the execution of King Louis XVI.

So it's no surprise that the Orléans have consistently been regarded as genuine royals, even though their house is no longer reigning (having lost their throne over 150 years ago, even before World War I).