The Cambridges are partying in London (and Kate borrows some FAB jewellery)

The Cambridges were out 'n' about in London on Monday night - looking lovely in formal attire.

They weren't quite out on the lash: she's pregnant with their third child, for one, while the soiree in question was actually being held in honour of his grandparents.

A post shared by RoyalTeaWithJam (@royalteawithjam) on Nov 20, 2017 at 3:24pm PST

Yes, the Queen and Prince Philip are now married for an incredible 70 years... so a load of royal types gathered at Buckingham Palace to toast the happy couple - who are both now in their 90s. [caption id="" align="aligncenter" width="672"] Kate a couple of weeks ago in the same dress[/caption] Duchess Kate wore an €885 Diane Von Furstenberg full-length black lace dress (she wore the same number to The Anna Freud Gala Dinner), but it was her choice of jewellery that really turned heads. https://twitter.com/RoyalFamily/status/932006703217995776 Opting for a stunning set of four-string pearls complete with an elaborate brooch clasp. The piece belongs to the Queen herself and the same choker was previously borrowed by Princess Diana, who wore it during the Eighties.

A post shared by Cambridge Fan (@princessdiana_cambridgesfan) on Nov 20, 2017 at 4:41pm PST

Wills and Kate arrived with Prince Harry - with both lads decked out in black-tie.

A post shared by ?? (@riah0719) on Nov 20, 2017 at 9:18pm PST

Others in attendance included Prince Charles and the Duchess of Cornwall, Prince Andrew, Prince Edward, and Princess Anne, as well as the Queen's grandchildren the Princesses Beatrice and Eugenie, and Peter Phillips and Zara Tindall.