Harry appeared via videolink
The Duke of Sussex could be heard saying to JJ and his professional partner Amy Dowden: "Nice tan JJ. Hi Amy it's really nice to meet you. When I first met JJ he was a shell of himself, but then to see you shine through Invictus, that was the start of an amazing journey."
Harry continued: "I'm so genuinely proud. You're not a dancer, proving that you can do anything you put your mind to, which is amazing."
Speaking about Harry, JJ said: "If Prince Harry had not created the Invictus Games, I would not have had that catalyst moment that changed my life forever."
Speaking exclusively to HELLO! this month, JJ revealed that he actually honed his skills at the wedding of his friend the Duke of Sussex.
"I remember dancing at Harry and Meghan's wedding. It was a bit of a reunion as there were a lot of mine and Harry's mutual friends there," said JJ, who first met Prince Harry when he was asked to be spokesperson for the inaugural Invictus Games.
WATCH: Strictly mics reveal what the stars said to one another during their routines
"I've been at Invictus opening and closing ceremonies with Harry when music is playing, but I can't remember if he was cutting any shapes," added JJ, as he and Amy joined us for an exclusive photoshoot to mark Remembrance Sunday.
"There's one thing I can say with confidence - I'm a better dancer than Harry now," he said, laughing.
JJ has certainly impressed viewers and judges with his moves on the Strictly dancefloor, leading fans to dub him this year's dark horse. And, he told us, the Duke is backing him all the way: "I've heard from Harry and he is immensely proud that I've taken the true heart of Invictus to the biggest audience possible on Strictly."
"JJ is what Strictly is all about," added Amy. "He gives it his all."