Tatiana Santo Domingo gets in theme for pal's lavish birthday party in the Swiss Alps

The hills were alive with royalty and hippies over the weekend. Princess Caroline of Monaco’s daughter Princess Alexandra of Hanover and daughter-in-law Tatiana Santo Domingo flocked to the Swiss Alps to celebrate a mutual friend’s birthday.

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Tatiana and Alexandra enjoyed a sister-in-laws' night out at the fashionable affair Photo: Instagram/@byconcepcion

The sister-in-laws attended the 30th birthday celebration of the late Greek shipping tycoon Stavros Niarchos’ daughter Eugenie Niarchos. Perhaps the highlight of the multi-day festivities took place on Saturday with a sixties soiree held at the luxurious five-star Hotel Kulm St. Moritz.

Tatiana, 32, and Alexandra, 16, were party-ready donning '60s-inspired attire. Andrea Casiraghi’s wife looked chic stepping out in a black and gold dress that featured a feather-trimmed collar and skirt hem, while Alexandra opted for a baby blue outfit.

Tatiana looked chic in a black and gold dress for the '60s party Photo: Instagram/@muzungusisters

Author Derek Blasberg shared various photos from the fashionable fête, which showed the guests’ interpretation of the psychedelic dress code. The birthday girl, who has the jewelry line Venyx, was photographed in one image blowing out her sparkler candles surrounded by friends including Tatiana.

Partygoers dressed in hippy-like clothing for the mountain celebrations Photo: Instagram/@evbousis

The colorful festivities continued into Sunday with a mountain party. Guests were treated to spectacular mountains views, perfect for the fashion group's stunning photo calls, in addition to a picnic setting, tents and bonfire.

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Unlike the other attendees, Alexandra elected for a toned down country look, wearing a natural-colored panama hat, white blouse and overcoat. The young royal was joined by her older brother and Tatiana's 32-year-old brother, Andrea Casiraghi, for a picturesque group shot.

Andrea Casiraghi (top left) posed for a photo with his sister Alexandra (bottom right) Photo: Instagram/@nevadagrosa

Also among those in attendance for the “Top of the World” fun was Italian stylist Giovanna Battaglia, who celebrated her society wedding in Italy last month with Monaco royalsPierre Casiraghi and Beatrice Borromeo.

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While Beatrice was no where to be found at the Switzerland soiree, her sister Matilde Borromeo appeared to enjoy herself with fellow party goers, which included model and her brother Stavros' girlfriend Jessica Hart, Sabine Getty, Missoni heiress Margherita Missoni and Roberto Cavalli’s Creative Director Peter Dundas.

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