How ‘completely crestfallen’ Prince William felt after learning about Kate Middleton’s cancer diagnosis

‘It wobbled him’

“It was devastating for him,” royal author Robert Jobson told Us Weekly.

Jobson’s book – Catherine, the Princess of Wales: A Biography of the Future Queen – was released this week. Jobson revealed that the Prince of Wales immediately felt “a lump in [his] throat,” which was followed by “the empty feeling in his stomach” after Kate shared the news with the world.

“It wobbled him,” Jobson said. “There’s no doubt about that.”

Kate has mostly stayed away from the public eye following her announcement. She wrote in a letter three months later that she was “making good progress” but had “good days and bad days” while going through the treatment.

She was seen in public for the first time after her cancer diagnosis announcement during the Trooping the Colour ceremony. Last month, Kate attended the Wimbledon tennis championships.

William has had his share of troubles as Kate battles cancer, what with his feud with his estranged brother, Prince Harry. Former royal butler Grant Harrold recently suggested that Harry and William are in private talks to sort out their differences. “Of course, a lot has happened, and a lot has to be resolved and sorted out. This may well be on track, but it may not have even been addressed yet,” he said.

A source previously told PEOPLE that William “doesn’t let Kate feel isolated” after her cancer diagnosis. The source described the Prince of Wales as a “very reliable, strong person” who is always “right beside” his wife amid her health woes. “This is about supporting her and her feeling supported. It is a joint effort. She doesn’t feel isolated at all,” the insider said.