A roadside police stop for a suspected stolen car has ended with a surprise marriage proposal for an Adelaide couple.

With the help of the South Australian Police (SAPOL), dentist Michael Yuan orchestrated a memorable moment his girlfriend Katie is sure to never forget.

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SAPOL officers pulled Mr Yuan over on what was said to be a check on a "suspect flag" on his car's registration.

But what was really happening was possibly one of the more unusual wedding proposals you'll see in a while.

As Mr Yuan was asked to get out of the vehicle, his girlfriend sat in the car puzzled by what was going on.

While the second SAPOL officer began to question her, and asked her to step out of the vehicle, Mr Yuan dropped to one knee and revealed an engagement ring.

Once she got over the shock, she responded with a resounding "Yes".