Princess Tatiana of Greece and Denmark — who once toiled with commoners in p.r. for designer Diane von Furstenberg before she left to marry Prince Nikolaos in 2010 — was in the Hamptons on Saturday signing copies of her new book, “A Taste of Greece.”

Raised in Switzerland, Tatiana has called Athens home since 2013, and proceeds from her new tome go to a food charity.

Spies said Tatiana signed books at the Greek Orthodox Church of the Hamptons then celebrated the tome and her husband’s 47th birthday at Tom Makkos’ Old Stove Pub restaurant, where billionaire John Catsimatidis was among 20 guests.

On Tuesday, Nikolaos — who was born just five years before the Greek monarchy was abolished in 1974 — was also spotted at Nello in Manhattan, “enjoying a four-course lunch . . . with his wife and friends . . . with lots of birthday toasts,” a spy said.

But while the royals celebrated, their economically challenged homeland said Monday thousands of refugees will be moved from squalid camps on the Aegean Islands to the mainland.