The popular prince, who has been heavily involved in the organising of the event for wounded, injured and sick servicemen and women, said it hadn’t been easy.
“There are times when we thought that we’re just never, ever going to get to the finish line,” he told The Express.
“If all the venues sell out, then I’m happy because it’s all about the atmosphere and making these guys feel really special.”
Harry, who turns 30 next Monday, also revealed the preparation involved in the Paralympic-style event had been “a real wake-up call”.
“Me and my big mouth, saying we’re going to fill the Olympic Stadium, we’re going to do this, do that,” he said.
“In my head it seemed very, very easy. In reality it’s been a real struggle.”
The Invictus Games will run in London between September 10 and 14.