The MTV show, which is a reboot of The Hills, began filming in August last year, which was four months before Cyrus and Hemsworth tied the knot.
In the most recent episode of the show, Carter is upset that her relationship with Jenner was rumoured to be "open", which she said was no ones business.
"It's tough for me to listen to Kaitlynn complain about people talking about her allegedly open relationship with Brody when we know she had a thing going with Miley. She already had something going on with her when these scenes were filming — maybe not physically, but definitely emotionally," reality star Spencer Pratt told Cosmopolitan.
Cyrus has denied being unfaithful during her relationship with Hemsworth.
In the episode, Carter tells her friends she wishes people had "common decency" when discussing other people's private lives, which Pratt claimed was hypocritical.
"I would love to know Liam Hemsworth's thoughts on Kaitlynn's recent displays of 'common decency'," he told the publication.
"You know what I call common decency? Getting it on at your Italian villa and not in front of the paparazzi."
Pratt is referring to the photos of Carter and Cyrus kissing on a yacht in broad daylight.
Brody recently shared a fiercely defensive Instagram post about his ex, wishing her "happiness".
"There is far too much negativity being directed at someone who I love and care about very much," he wrote. "I feel the need to set the story straight. Kaitlynn and I have been best friends for 6 years, and we continue to be.
"We, like many others before us and many after us, grew in different directions over those same 6 years. Kaitlynn is a wonderful person, beautiful and fun to be with, always a positive force in my life.
"We decided the best move for both of us was to keep our love for each other strong but move forward separately with our lives."
The Hills: New Beginnings has been renewed for a second season.
