"I knew the moment I met you, you were the man of my dreams and I wanted to be with you forever," Johnson wrote on Instagram, sharing two photos of the proposal in Venice. "Babychka Мой любовь thank you for making my fairytale come true today! Cannot believe I get to call you my FIANCÉ!!!!"
"I can't wait to make you my wife," Chmerkovskiy wrote. He shared the same two photos.
The two lovebirds dated until 2016, but reunited last year. They dropped several hints about getting married last month.
On May 8, a fan tweeted a GIF of Johnson, and the 32-year-old Chmerkovskiy replied, "I should def put a ring on it."
In an interview with Entertainment Tonight, Johnson joked, "Time's a-ticking."
"We'll see [if engagement is in the cards anytime soon]," the 24-year-old Johnson wrote. continued. "We both have very big things happening right now, so we'll let that ride over... maybe we'll go to Fiji!"
Johnson previously appeared on So You Think You Can Dance before joining DWTS as a troupe member for season 18. She became a pro for Season 23, paired with Jake T. Austin. Last month, she won her first Mirror Ball Trophy as Adam Rippon's partner.
As for Chmerkovskiy, he has been a member of the DWTS family since season two and won the Mirror Ball Trophy with Rumer Willis and Laurie Hernandez. His older brother, Maksim Chmerkovskiy, married fellow DWTS pro Peta Murgatroyd last year. They also have a son, Shai Aleksander, who was born last year.
Earlier this year, the Chmerkovskiy brothers and Murgatroyd toured the U.S. together, which meant Chmerkovskiy could not participate in DWTS this spring. However, he still helped out Johnson and Rippon, flying to Los Angeles to get them ready.
"He's flown in and helped Adam just with some guy stuff and it's been incredibly helpful," Johnson told ET. "He texts me almost every, single day and asks me to send him videos, so he can give me some notes and just see what's going on. It's so sweet."
Chmerkovskiy told ET it was "hard" for him to watch Johnson dance with other men.
"I would never want to compromise my artistry, you know, because I wouldn't want to make my significant other feel uncomfortable," he said. "But I think it's also, this is part of the new chapter in my life and, you know, it takes some sacrifice to have a healthy relationship. And, you know, you gotta be willing to make those sacrifices and I'm definitely willing to make certain sacrifices to make it work."
DWTS will return for a 27th season in the fall on ABC. Chmerkovskiy's book, I'll Never Change My Name, is also now available.