"That uncontrolled, unhinged side that we get to see this season of Billy was a lot of fun," Montgomery said while in Sydney. "The scale of everything was just incredible."
The 24-year-old star has encouraged fans of the Netflix series to stick with Billy until the end of the season, even though it will be extremely hard.
"I think they're going to hate him more and more and more until the payoff at the end of the season," Montgomery said of the sci-fi show. "I can just say the payoff is worth it. Hold out until episode 8 because it's so worth it. I'd love to see the reaction. That's the most I can tease."
The new Stranger Things season is set in the summer of 1985, and it follows Eleven (Millie Bobby Brown) and her friends (played by Finn Wolfhard, Noah Schnapp, Gaten Matarazzo, Caleb McLaughlin and Sadie Sink) as they fight off the upside down and the threats that follow, in their town of Hawkins.
In fact, the Stranger Things star got to spend a lot more time working alongside Millie this season, and as expected, he had nothing but amazing words for the young actress.
"She's an old soul. She's got a lot of maturity for her age and I admire that, definitely. She's super committed in the scenes," the actor told the publication. "It gets very emotional between us towards the end of the season and I felt like she could really meet me at that level."
Stranger Things season 3 premieres on Netflix July 4. Here are all the different times in Australia.