Dove Cameron Dishes on Costar Fiancé Ryan McCartan's 'Perfect' Proposal: 'It Was Very Spur-of-the-Moment'

Dove Cameron knew her Liv and Maddie costar Ryan McCartan was the one – but she was completely caught off guard when he popped the question!

“We were both very clear with each other that it was like, ‘I know you’re my person. You know you’re my person. There’s nobody else,'” Cameron told PEOPLE at the 23rd annual Race to Erase MS gala in Beverly Hills on Friday. “But I knew he wanted to get married young – he had told me that. He was like, ‘That’s what I want as my life plan.'”

But when it came to actually proposing, “he didn’t hint at it,” the actress says. “It was very spur-of-the-moment. It was perfect.”

Although the Disney star, 20, is remaining mum on how her fiancé, 22, popped the question – which they announced earlier this week on social media – she does admit “it was more romantic and bohemian than traditional.”

McCartan didn’t let her family in on his plans by asking for permission, she explained, but they were already sold on the actor as ideal husband material.

“He had the permission sort of after the first year that we were together,” she says. “My mom was like, ‘If you don’t marry him, something’s wrong with you!’ My whole family was like, ‘We like him more than you, so figure it out.’ ”

She revealed that once she said “yes,” the couple’s relationship immediately shifted into a new gear.

“It’s like that weird thing where people are like, ‘How does it feel to be a year older today?’ and you’re not any different,” she explains. “But then there’s always like those once-every-six-year-birthdays where you’re like, ‘Whoa, I woke up, and the world was different around me.’ And it was like that.”

And this revelation took the couple – who together make up the musical duo The Girl and the Dreamcatcher – by surprise.

“Because we already knew we wanted to get married one day, I didn’t expect it to change anything,” she added. “But ‘fiancé’ and ‘boyfriend and girlfriend’ is worlds apart. I literally feel like I’ve never been so calm before. I feel rooted to the ground. I feel good.”

The actress said she and McCartan felt like marriage was inevitable a month into their relationship, which began shortly after they met on set in 2013.

“We had this stupid moment, a stupid cheesy moment in my dressing room where he looked at me and it was all like dramatic – it was so dramatic! He stared at me, and I was like, ‘What?’ And he was like, ‘Oh I don’t know. I can see myself … nothing.’ And I was like, ‘I can see myself, too.’ And literally from then on, we’re like, ‘Are we going to get married? Alright, cool.’ And it’s been like three years, and now we’re engaged.”

She explained that neither of them are in a rush to lock down a date and other details, and they’re not concerned about their relatively young ages, either.

“I have never felt my age, and he hasn’t either,” she says. “I have always felt like I was just sort of waiting to catch up to the rest of myself. So I feel like I’m 28, maybe, and I’m sort of like, ‘Why is everybody freaking out?’ But I’m 20, he’s 22. I’m thinking by the time we’ll get married, he’ll be 25, I’ll be 23.'”

“It’ll be a while because we have projects lined up,” she added. “I don’t want to hate the process. I want to take my time.”