(CNN) -- Ashton Kutcher's quiet romance with Mila Kunis has reportedly blossomed into an engagement.
The former "That '70s Show" co-stars have never been shy about PDA since they began dating in 2012, but neither one has talked much about the relationship.
Reps for both actors have been mum, with only a telltale photo of a diamond ring on Kunis' left hand to fuel speculation she and Kutcher will soon be tying the knot.
But how did these two go from friends and co-workers to a couple? Here's a recap of the love story:
1998: Kutcher, then 20, landed a role in "That '70s Show," the Fox comedy about a high school kid growing up in Wisconsin during the late 1970s. Kutcher was the ditzy pretty boy Kelso, and Mila Kunis, at 15, was Kelso's on-again, off-again girlfriend, Jackie.
At the time, Kutcher was in a relationship with a pre-"Mad Men" January Jones, but working together definitely helped Kutcher and Kunis bond.
The actress told People magazine in 2001 that Kutcher, a former model, was her first kiss.
"I was so nervous and uncomfortable," Kunis recalled. "I had the biggest crush on him."
Kutcher, on the other hand, insisted in 2001 that he was the nervous wreck.
"She acted so cool. She seemed as if she'd done it a thousand times," Kutcher told the magazine. "I was the one with the butterflies in my stomach. I mean, here's this little girl, and I have to kiss her. It was nerve-racking."
2002: With "That '70s Show" turning both Kutcher and Kunis into household names, their private lives became the interest of the public. Kutcher moved on from Jones and began dating actresses such as Ashley Scott and the late Brittany Murphy.
Meanwhile, Kunis struck up a relationship with Macaulay Culkin of "Home Alone" fame in 2002, and their relationship lasted for eight years.
2005: By now, Kutcher had fallen for Demi Moore, nearly 16 years his senior, and they wed in a private Kabbalah ceremony in 2005.
2006: As "That '70s Show" came to an end, Kutcher and Kunis had apparently forged an enduring friendship. When they were first spotted spending a lot of time together in 2012, Kunis' rep brushed off the romance reports by saying that "they have been friends for years."
2011: Kutcher and Kunis moved on personally and professionally after "That '70s Show." Kutcher had been trying his hand in films with romantic comedies such as "What Happens In Vegas" (2008), "Valentine's Day" (2010) and "No Strings Attached" (2011).
In 2011, Moore released a statement she was ending her marriage to the star. "It is with great sadness and a heavy heart that I have decided to end my six-year marriage to Ashton," she said at the time. "As a woman, a mother and a wife there are certain values and vows that I hold sacred, and it is in this spirit that I have chosen to move forward with my life."
April 2012: The April following his separation from Moore, Kutcher and Kunis began spending a large amount of time together. They were seen dining out and going furniture shopping, and they reportedly went on a weekend trip.
A "Kutcher source" wasn't surprised by the turn of events, telling People magazine that while nothing happened during "That '70s Show," Kutcher "was always talking about how beautiful she is. But she was with Macaulay (Culkin) for a lot of that time and also just generally gave off a not interested vibe."
Yet when "Extra" asked Kunis what was going on with Kutcher, the actress called the dating rumors "absurd" and said, "A friend is a friend."
September 2012: At some point, these "friends" found something more. While Kunis insisted she was having a hard time finding a date in July 2012, paparazzi photos told a different story. She was seen kissing Kutcher in New York's Central Park that September, a month after the two were rumored to have taken a vacation to Bali and two months after they seemed very into each other at a wrap party for his Steve Jobs biopic, "Jobs."
December 2012: As their relationship became more apparent, Kunis and Kutcher headed on a trip to his hometown in Iowa for the holidays.
February 2013: While on Ellen DeGeneres' talk show, Kunis was visibly flustered when the host grilled her about her relationship with Kutcher.
"Have you talked to him at all? When was the last time you talked to him?" DeGeneres asked.
Kunis, failing to keep a straight face, replied, "Um, you know, it's been, give or take, a couple minutes."
March 2013: Last spring, Kutcher explained his reluctance to talk about what had become a pretty obvious love affair. "You know, I've learned the hard way how valuable privacy is," he told Elle magazine in its March 2013 issue. "And I've learned that there are a lot of things in your life that really benefit from being private. And relationships are one of them. And I am going to do everything in my power to have this relationship be private."
November: Following rumors that Kutcher and Kunis were engaged in September -- which turned out not to be true -- Kutcher became officially single again. Two years after Moore initially announced their marriage had ended, Kutcher's attorney filed a document in court that made their final divorce settlement official.
January and February: As cameras kept catching Kutcher and Kunis in the act -- they were seen kissing courtside at a Los Angeles Lakers game -- Kunis began to open up a bit more about their bond. In a February interview with Cosmopolitan magazine, Kunis described her ideal date night:
"We have a thing called white T-shirt night, and it's when you wear jeans and a white T-shirt and you go on a date," she said. "Nothing fancy, it's just something that you love to do."