The purge of Princess Srirasmi's family over the past 10 days has been widely reported in Thailand.
However, until now the severity of the lese majeste law criminalising any critical comment about the monarchy meant that no Thai media had pointed out the family connection.
The princess's uncle, a senior police general, was arrested over accusations of amassing vast wealth through smuggling and gambling rackets.
Four of her siblings and two other relatives have also been held.
The office of Crown Prince Vajiralongkorn has now sent a letter to the interior ministry ordering her family to be stripped of the royal name he bestowed on them when he married her.