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The princess is a former Olympic swimmer, which her dad Michael Wittstock believes has instilled a sense of perseverance that will benefit her in coming months. "Based on the way she used to train, I know she's tough and will get through this and come out much stronger," he told South Africa's YOU magazine on Friday.
Charlene, 44, traveled to her family's home country in Africa in May. Shortly after, complications from a prior medical procedure grounded her from flying due to ear, nose and throat issues, and she underwent multiple corrective surgeries throughout the summer so she could return to Monaco to be with her husband, Prince Albert, and their twins, Prince Jacques and Princess Gabriella, who turn 7 on Friday.
Watch: Prince Albert Tells PEOPLE Princess Charlene Is in a Treatment Facility: 'She Realized She Needed Help'
Though Michael and Charlene's mother, Lynette, were unable to visit a "vulnerable" Charlene during her time in South Africa due to an abundance of caution surrounding the COVID-19 pandemic and Charlene's health issues, he says, "We spoke regularly on the phone, and I speak with the twins. We have a great relationship."
Charlene, 43, Albert, 63, and several members of Charlene's immediate family agreed with her decision to seek medical care just days after she returned to Monaco on November 8.
The prince told PEOPLE in an exclusive interview that his wife was experiencing "exhaustion, both emotional and physical," and that several weeks of clinical care were advised.
After Charlene made the difficult decision to separate from her family once again, the twins stood on the balcony of the palace waving homemade signs of support on Monaco's National Day, November 19. Gabriella's sign read: "We Miss You Mommy," and Jacques' read: "We Love You Mommy."
VALERY HACHE/AFP via Getty Images Prince Albert with twins Princess Gabriella and Prince Jacques
This year's outdoor ceremony was intended to be a welcome home celebration for Charlene and included several elements commemorating the couple's 10th anniversary.
Instead, with their mother away, Jacques and Gabriella's special bond was on display. At one point, Jacques reached over and sweetly held his sister's hand. Gabriella then reached for her brother's hand moments later.
A palace source told PEOPLE at the time, "Prince Albert said he wanted today to be as close to a normal National Day as possible — and in particular, as much as can be for the children."
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