Princess Charlene's children revealed how much they're missing their mother as Prince Albert confirmed that his wife is receiving treatment in a facility "outside of Monaco".

As six-year-old twins, Prince Jacques and Princess Gabriella, joined their father on the balcony of the Prince's Palace for Monaco's National Day on Friday, they held up a drawing surrounded by red hearts, which read: "We miss you mommy."

Prince Albert, 63, reveals that a family-style intervention took place with Charlene, 43, following his trip to Dubai last week. He told PEOPLE magazine: "I sat her down with her brothers and a sister-in-law. She had already made her decision, and we only wanted her to confirm it in front of us. She wanted this. She already knew the best thing to do was to go and have a rest and have a real medically framed treatment. And not in Monaco. For privacy reasons, it would have to be someplace outside of Monaco."

He also dismissed further speculation about Charlene's health, telling the magazine: "Because I know there are rumours out there, let me say: This is not COVID. And it's not cancer-related. It's not a personal relationship issue. And if you want to discuss another speculation, it isn't related to plastic surgery or facial work at all."

In relation to rumours about their marriage, Albert reiterated: "These are not problems within our relationship; not with the relationship between a husband and wife. It's of a different nature."

Princess Gabriella and Prince Jacques dislayed a heartfelt sign

He also said that he and the couple's children planned to visit Charlene but that he couldn't give "any kind of time frame on that".

Asked about how he's faring, Albert told PEOPLE: "This is usually the busiest time of year. I don't have time to be going around with a too-sad face. I'm okay. Of course I'm saddened by the situation, but I know she's in a good place now. That she'll recover and that this is the best place for her."

Princess Caroline and Princess Stephanie joined Monaco's National Day 

Earlier this week, the Palais Princier confirmed that the princess would not be present for the celebrations, releasing a statement that read: "Their Serene Highnesses have both decided that a period of calm and rest is necessary to ensure the very best recovery for Princess Charlene's health.

"Having battled with poor health over the past few months, the Princess is currently convalescing and will continue to do so for the coming weeks, allowing her time to recover from a state of profound general fatigue. In order to protect the comfort and privacy essential to her recovery, the Princess' location will remain strictly confidential."

Charlene's move to a treatment facility comes less than two weeks after her return to Monaco to be reunited with her family. The princess spent six months grounded in South Africa due to an ear-nose-throat (ENT) infection, during which time she underwent operations.

Albert was joined by his sisters, Princess Caroline of Hanover and Princess Stephanie, for Monaco's National Day celebrations, attending a Thanksgiving mass before watching the festivities from the palace.