Nicky's older sister, Paris Hilton, was naturally also in attendance, rocking a glittery black and silver dress with a plunging neckline.
Nicky also posted a mirror selfie in the chic ensemble and captioned it, "When you turn your Dolce into maternity wear."
A source close to the youngest Hilton daughter told ET that she is due this summer. It will be her first child with husband James Rothschild, an heir to one of Europe's greatest banking families. Together since 2011, the couple married in a lavish ceremony at Kensington Palace in London last July.
Check out more shots of Nicky's gorgeous Valentino wedding gown in the video below.