Christina Aguilera, Eva Herzigová and Princess Charlene lead a glamorous guest list at royal gala

Christina wore a dramatic floor-length black gown featuring a daring plunging neckline, thigh-high split and an oversized crystal-encrusted embellishment at the neck. The 'Beautiful' singer teamed the glamorous look with pointed black heels and sparkling jewellery, while wearing her platinum blonde hair swept up at the crown before falling in voluminous curls over one shoulder. She completed the look with fluttery lashes, rosy cheeks and a glossy nude lip. Christina was one of the evening's performers, alongside Plácido Domingo and Sister Sledge.

Princess Charlene delivered another elegant royal fashion moment as she joined her husband, Prince Albert, for the milestone evening. The 48-year-old royal wore a sleek floor-length black gown featuring a sheer, intricately embellished neckline finished with dramatic beaded fringe. She carried a small sparkling clutch and wore her blonde hair swept into a chic updo. Prince Albert, 68, was equally polished beside her in a traditional black tuxedo and bow tie as the couple welcomed guests to the celebration marking 20 years since the Prince established his environmental Foundation in 2006.

Eva Herzigová looked sensational as she attended the gala with her husband, Gregorio Marsiaj. The Czech supermodel, 53, showcased her statuesque figure in a strapless black gown with a dramatic plunging sweetheart neckline and thigh-high split. Keeping the monochrome look polished, she added pointed black pumps and dazzling diamond earrings and a necklace, while styling her hair in soft Old Hollywood-inspired waves. Gregorio complemented his wife in a crisp white double-breasted dinner jacket, black trousers and bow tie.

Monica Bellucci proved the enduring appeal of classic black as she stepped out in a sophisticated floor-length gown. The 61-year-old actress opted for an elegant asymmetrical design with a draped bodice, long sleeves and a subtle cut-out detail at the waist. She added extra sparkle with a diamond necklace, while her signature brunette locks fell over her shoulders in loose waves with a full fringe framing her face. The Italian star was one of the gala's guests of honour, alongside Hollywood actor Richard Gere.

Isabelle Huppert stood out from the evening's sea of black in a head-to-toe scarlet ensemble. The French actress, 73, paired a structured red jacket with a coordinating top and dramatic wide-leg trousers that swept the green carpet. She finished the striking tonal look with glittering hoop earrings and layered necklaces, while her shoulder-length red hair was styled in soft, tousled waves. A classic red lip brought the whole look together as Isabelle joined fellow film stars for the Foundation's milestone celebration.

Richard Gere looked effortlessly dapper as he arrived in classic black tie. The 77-year-old Pretty Woman actor wore a sharply tailored black tuxedo with satin lapels, teamed with a crisp white shirt and black bow tie. His silver hair provided the finishing touch to the timeless look as he posed for photographers on the green carpet. Richard attended as one of the night's guests of honour, with the gala also highlighting a collaboration between the Prince Albert II of Monaco Foundation and the Richard Gere Foundation focused on biodiversity.