Princess Isabella of Denmark, 16, wears her mother Princess Mary’s diamond and amethyst earrings and silver clutch at Prince Christian’s 18th birthday party

Princess Isabella of Denmark oozed elegance as she arrived at her brother Prince Christian’s 18th birthday gala at Christiansborg Castle.

The 16-year-old opted for a cobalt blue satin dress from Safiyaa, featuring a strapless neckline, a pleated bodice and a full skirt, accessorized with a flowing scarf.

She wore her mother, Crown Princess Mary’s silver J.Furmani clutch and dazzling amethyst and diamond earrings.

The young royal attended the glamorous event alongside her sister Princess Josephine, 12, and brother Prince Vincent, 12.

They joined their parents, Prince Frederik and Princess Mary, along with Prince Christian, before greeting Queen Margrethe II.

Princess Isabella’s dress was accessorized with a pair of earrings from her mother’s personal collection.

They featured a briolette amethyst suspended from a row of sparkling diamonds, making for a statement piece.

These earrings have been worn by Princess Mary since early 2006 and are believed to have been a gift to mark the birth of Prince Christian in late 2005.

Amethyst is also the birthstone of February, making it a fitting gift.

Mary has been seen wearing these earrings on a number of occasions, from daytime engagements to formal events. often combining them with her wedding tiara.

Princess Mary wears her diamond and amethyst earrings at a dinner celebrating the 60th birthday of King Carl XVI Gustaf of Sweden in Stockholm (photo April 2006)

Princess Isabella arrived at the glamorous event with her sister Princess Josephine, 12, who wore a chic jumpsuit by Jesper Høvring

Prince Christian and his parents beamed as they greeted Queen Margrethe II

Isabella sat with friends at a round table decorated with colorful flowers

A host of European royals attended Prince Christian’s birthday gala, including his godparents Crown Princess Victoria of Sweden and her husband Prince Daniel, along with their 11-year-old daughter Princess Estelle

Princess Josephine looked equally chic as she arrived at the gala in a navy blue jumpsuit from Jesper Høvring and metallic gold pumps from Anonymous Copenhagen.

A large number of European royals were present, including Christian’s godparents Crown Princess Victoria by Sweden and her husband Prince Daniel, together with their 11-year-old daughter Princess Estelle.

The prince’s other godfather, Norwegian Crown Prince Haakon, was also in attendance with his wife Crown Princess Mette-Marit and daughter Princess Ingrid Alexandra, 19.

Earlier that day, Christian delighted the crowds gathered outside Amalienborg Castle in Copenhagen to celebrate the heir apparent’s 18th birthday.

Looking dapper in a gray checked suit and navy blue tie, Christian was in his element as he waved to the crowd.

He was then joined by his father Crown Prince Frederik and grandmother Queen Margrethe – before being joined by his mother Princess Mary and siblings Princess Isabella, Prince Vincent and Princess Josephine.

Australian-born Princess Mary looked stylish in a powder blue coat dress to protect herself from the chilly Danish autumn, while Queen Margrethe opted for a bolder shade of purple.

Ahead of the festivities, sympathizers gathered in Copenhagen and the royal family shared a series of heartwarming childhood photos of Christian.

Prince Christian of Denmark was delighted with the crowds who gathered outside Copenhagen’s Amalienborg Castle to celebrate the heir apparent’s 18th birthday

The royal family shared some never-before-seen photos of the prince during his childhood

Photos of baby Christian were also shared

The never-before-seen footage, taken by the prince’s parents, documented a number of private memories.

The photos include a trip to Paris, a visit to Australia, skiing, tennis and ‘special moments with grandpa’ – the late Prince Henrik.

Other members of the royal family, including his cousin Count Nikolai, shared happy birthday messages to the future king.

The Danish Royal House also released an official birthday portrait of Prince Christian – taken by his mother – along with a schedule of events.

Meanwhile, flags were hoisted throughout the country in honor of the future king.

For the first time, October 15 has been declared an official flag day. From now on, all state buildings and state ships in Denmark will fly the Dannebrog on Prince Christian’s birthday.