"We were determined. I've always known since I was little I had the same birthday as Prince Charles."
The pair have celebrated their birthdays together for years, and have always acknowledged Prince Charles' birthday too, said Mrs TeWake.
"We always say happy birthday to Prince Charles too, he couldn't be here but he sends his love and his hoping to catch up with us some day," said Mrs TeWake.
Mrs TeWake has had a brush with royalty before.
When Queen Elizabeth II was on her 1953 tour, Mrs TeWake sneaked through security guards to touch the Queen's frock.
Mrs TeWake and Mrs Thomas are eagerly awaiting the letter outlining their dress code.
Masterton sheep and beef farmer Ross McLachlan said his outfit was "more my wife's department".
Mr McLachlan said he felt lucky to have been selected.
"I'm quite happy to enter into the spirit of the occasion."