The behind-the-scenes clip showed William practicing pledging his allegiance to his father.

So help me God."

Next, William was required to touch the crown and kiss his father and King on the cheek.

King Charles III looking at Prince William

Afterward, William can be seen trying to fasten a pin onto Charles' robes.

“It’s quite a small catch,” the prince said, frustrated at the finicky bauble.

“On the day, it’s not going to go in, is it?”

Prince William touches King Charles' crown during coronation

“I know my limitations,” Charles said.

“But at least I have my glow stick,” viaBusiness Insider.

He tried to do his best" (viaYahoo Entertainment).

Young Prince William, King Charles, and Prince William stand outside together

“My father’s first words on entering Westminster Abbey yesterday were a pledge of service.

Pa, we are all so proud of you,” perABC News.