Even so, it's a lot for a 10-year-old to handle.
George has already lost his great granny and great-grandfather on top of the scary news that his grandpa King Charles is also battling cancer.
"George has been through the mill these past few weeks and he's old enough to be aware of what's going on. It's been a lot for him to handle, and he's sticking close by his Dad's side," our palace source says.
"William has been an absolute pillar of strength for all of them, but sadly, he also knows exactly just how George must be feeling. George is only five years younger than he was when he lost his own mum."
For a man who lost his own mother when he was just 15 years old, there can be no doubt that Kate's health battle has triggered painful memories for Prince William.
"He is deeply in shock over this," reveals a palace source.
We're told Kate made her cancer announcement alone because she was worried her husband might break down on camera due to the love he has for her.
Wills faced criticism for not sitting beside Kate during her video statement, but it was a choice she made deliberately. She wanted to inspire others with her strength - and protect William.
WATCH NOW: Prince George and his siblings join their mother volunteering at a baby bank.
"It's triggered his previous trauma point from when his mum died," says our source. They add that Wills is still processing the "anger and hurt" he feels over the indiscriminate nature of cancer.
"He can't talk to the only person who might understand this [his brother Harry]. so it's easy to see why everyone is concerned. He's hurting and suffering alone," says the source.
However, our source adds that William will draw on his "military training and inner strength to be there for Kate."
He was famously a shoulder for his mum to lean on during her divorce and now he'll do the same for his wife.
"Diana would be so proud of him," our source shres.
With Kate optimistic about her prognosis and future, she and William have worked hard to privately reassure and counsel George, Charlotte, and Louis, but cancer is a terrifying word to anyone, let alone your own kids.
"William is protective of George right now, and as helpless as they all may feel at the moment, he's showing George how to keep calm and carry on," our source adds.