Monaco royals under pressure to reveal whether marriage is 'on the rocks'

Prince Albert of Monaco is facing growing calls to come clean over whether his marriage to Princess Charlene is on the rocks after she failed to return to the tiny principality to celebrate their tenth wedding anniversary.

Princess Charlene, 43, has not returned to Monaco since March after leaving for her native South Africa on a conservation trip.

Her departure came shortly after reports that Albert, 63, was facing a paternity suit over an alleged love child born in the early years of their relationship. Albert already supports two illegitimate children.

Watch: Princess Charlene Makes an Elegant Entrance in Glittering Gown at Monaco's Red Cross Ball Gala

The couple, who share six-year-old twins Princess Gabriella and Prince Jacques, were set to celebrate their 10th wedding anniversary on July 1, but Princess Charlene failed to return.

According to palace officials, the only reason she was staying away was because doctors had advised the former Olympic swimmer for South Africa “not to travel to Monaco” due to complications from a "serious" ear, nose and throat infection. Earlier this month, Prince Albert said she had undergone an operation and was "resting".

Seeking to quash rumours of an impending split, Prince Albert flew out to South Africa and the pair posted Instagram pictures on August 25.

However, Madame Figaro, the respected conservative women’s weekly, said their "strained embrace", in which Princess Charlene looks drawn, "failed to convince the Monegasques" amid reports she is looking for a house in Johannesburg.

The magazine called for the growing "malaise" over her absence to be cleared up.

"How long can she remain away from her children, her duties?," asked the magazine. "How long will the fight against rhinoceros poaching remain the Princess of Monaco's top priority? How long will Albert II of Monaco go on bearing this affront, which is becoming ridiculous?"

One "well-placed source" told the magazine Voici back in June: "Everyone has started thinking she won't come back."

Last month, France's best-connected royal pundit and Macron's heritage tsar, Stephane Berne, wrote an article for Paris Match headlined: "Albert and Charlene on the verge of splitting up?"

The royal couple met in 2000 at a Monaco aquatic competition and married at a star-studded ceremony in July 2011.

However, questions over their relationship swiftly surfaced following reports she had bolted two days before her royal nuptials.

It was alleged she tried to flee home to South Africa three times one point taking refuge inside her country's embassy in Paris. Her tears and mournful demeanour at the ceremony did nothing to assuage the rumours.

"Lots of people go the impression it was an arranged marriage, it’s true," said Philippe Delorme, historian and author of The Finest Hours of the Grimaldis and Monaco.

"Albert chose a wife who resembled his mother, and Charlene clearly felt very ill at ease in this Grace Kelly role they wanted her to play," Mr Delorme told Madame Figaro.

Princess Grace died in a car crash in 1982.

"As Karl Marx put it: History repeats itself, first as tragedy, second as farce," he said.

Watch: Princess Charlene Shared the First Picture of Her Twins Since Prince Albert’s Self-Quarantine