Pregnant Princess Beatrice dons bow-tied velvet LBD for night out with Princess Diana’s nieces

Princess Beatrice got a head start on holiday dressing.

The royal, who is expecting her second child with husband Edoardo Mapelli Mozzi, donned Rebecca Vallance’s festive Eliana midi dress ($920) to celebrate the Australian designer’s new collection in collaboration with Nicky Hilton, who co-hosted the event.

With its soft material, dramatic bow details, and high-shine crystals, the show-stopping number has all the makings of the perfect holiday party look.

Princess Beatrice supported Nicky Hilton’s collaboration with Australian designer Rebecca Valance, sporting a black velvet and sequin design on Tuesday night. Dave Benett/Getty Images for Estée Lauder The royal, who is pregnant with her second child, added a black tank top underneath the look. Sam Simpson/Dave Benett/Getty Images for Rebecca Vallance

She appeared to have layered a matching black tank top underneath, adding a bit of coverage to the skin-baring dress.

The royal stepped out in equally glitzy crystal-encrusted black satin heels ($1,995) from Roger Vivier.

Bea rounded out the festive ensemble with a black clutch, small circular earrings and dainty gold bracelets — including one with a gold “B” charm.

She announced her pregnancy on Oct. 1. Beatrice shares 2-year-old daughter Sienna with husband Edoardo Mapelli Mozzi. Dave Benett/Getty Images for Estée Lauder She posed with Vallance and Hilton, with other celebs in attendance including Amelia and Eliza Spencer. Sam Simpson/Dave Benett/Getty Images for Rebecca Vallance Eliza and Amelia — seen here on the left and right, respectively — were joined by cousin Kitty Spencer at a separate event later in the night that Beatrice also attended. Dave Benett/Getty Images for Estée Lauder

Princess Diana’s nieces, identical twins Amelia and Eliza Spencer were also in attendance at the party, wearing a red sequined long-sleeved look and a chic black LBD, both from the line, respectively.

Later in the evening, Beatrice and the Spencers left the Hilton-helmed event — and were joined by Kitty Spencer, Amelia and Eilza’s first cousin — for a dinner hosted by Estée Lauder and Harrods.

Beatrice announced her pregnancy on Oct. 1 and shares 3-year-old daughter Sienna with Mozzi. She also serves as stepmom to Christopher Woolf, Mozzi’s 8-year-old son from a previous relationship.

Earlier this year, Prince Andrew and Sarah Ferguson’s elder daughter was named the best-dressed person in Britain by Tatler magazine, proving she’s come a long way since her maligned royal wedding hat in 2011.