Beyonce and Jay Z's new twins have been named Rumi and Sir Carter, it has been reported in the United States.
According to the showbusiness website, TMZ, the couple have filed trademarks to protect their names.
Beyonce and Jay Z - real name Shawn Corey Carter - went through the legal formalities on Friday. Their older sister is called Blue Ivy.
Rumi, the website reported, was a homage to a 13th-century poet. The choice of Sir Carter remains a mystery.
An array of goods are covered by the trademarks including strollers, mugs, ribbons, rattles and babies' teething rings.
The couple used the same company when they registered Blue Ivy as a trademark.
They are, of course, honouring a long-standing pop tradition of giving offspring esoteric names.
Chris Martin and Gwyneth Paltrow called their daughter Apple. Alice Cooper opted for Calico for his daughter.
David and Angie Bowie chose Zowie. Now a well-known film director, he is known as Duncan Jones - the surname being Bowie's real family name.
Few could top the late Frank Zapper who named his children Moon Unit, Dweezil, Ahmet, and Diva Muffin.