King Charles is being a supportive father-in-law to Kate Middleton as she recovers from abdominal surgery. His Majesty and Queen Camilla reportedly visited the Princess of Wales at the London Clinic, which is the same hospital he’s expected to have his corrective procedure done. OK! previously reported Charles had an appointment to treat his enlarged prostate while Kate heals from her operation. “The Queen has told him he needs to slow down a bit,” a source told an outlet. Before Charles ascended to the throne, he was the longest-reigning Prince of Wales and he transformed the role’s significa…