King Charles and Kate Middleton are both battling cancer, and though it has led to a rather turbulent time for the royal family, their diagnoses has allowed them to develop and even closer bond while they work hard at getting better.

“He has always had a very good bond with her. I don’t think it is presumptuous to say that she is like the daughter he never had,” royal biographer Sally Bedell Smith tells People. “He shares with William an impulse to protect her. They are in this together, Kate and the King.”

It’s not surprising that Kate and Charles are connecting with each other even more at the moment — they are “two patients going through a common health experience,” a royal source told the outlet, noting they “are bound to have a close connection.” The source added they “imagine there was some comfort [for Kate] in seeing that it was possible to balance some private information without there being an imperative to share all.”

The report comes after royal source revealed that Charles and Kate had a heartfelt meeting with each other after her cancer video announcement. Speaking with Entertainment Tonight, royal expert Katie Nicholl revealed that “the king had lunch with Catherine on Wednesday in Windsor after she recorded [her video] message.” The outlet also reports that Charles visited his daughter-in-law while she was being treated for her abdominal surgery at The London Clinic.

“That’s quite special. I don’t think you get to have many one-to-one audiences with the king,” Nicholl added. “I think that’s an indication of how close they are, and certainly this shared experience, this shock double cancer diagnosis will only bring them closer.”