"We were both in tears ... I genuinely had no idea he was going to do that," Roberts, 36, said of the romantic gesture.
So who is the woman who managed to steal Hasselhoff's heart? Here are five things to know about Roberts:
1. She was born in the United Kingdom
Roberts was grew up in a small town in Wales with her parents and three siblings. Before meeting Hasselhoff, 63, and moving to Los Angeles, Roberts worked as a sales assistant at a popular U.K. department store called Debenhams.
2. She met Hasselhoff while he was signing an autograph for her
Roberts spotted Hasselhoff in a hotel lobby while he was in town filming auditions for Britain's Got Talent, on which he was a judge at the time. When Roberts approached him and asked for a photograph, Hasselhoff agreed on one condition: She had to give him her phone number. A few days later, the two went on their first date together – and have been inseparable ever since.
3. She loves to travel
A quick scroll through Roberts Instagram and one thing quickly becomes clear: She doesn't stay in one place for long. The Welsh beauty has snapped romantic pictures alongside Hasselhoff in numerous exotic locations including Australia, Africa and Sweden, among others.
4. She's a total beach bum
When she's not jet-setting across the globe, Roberts can usually be found lounging on the beach – proving she fits right in with Hasselhoff's Baywatch lifestyle.
She even posted an Instagram snap showing her in that classic red swimsuit while on the beach with Hasselhoff seemingly in character from his Baywatch days.
"Playing around!" she captioned the shot.
5. She's close with the actor's two daughters
Throughout her five-year relationship with Hasselhoff, Roberts has formed a close bond with his two daughters, Hayley, 23, and Taylor, 25. In fact, they were totally on board when their father decided to pop the question to Roberts.
"I told my girls what I was going to do and they were both really supportive," he said. "It's tough. No one wants to see their parents split up. But they love Hayley and they're just happy for me."