One of the rarest watches in the world just sold for $5 million and became the most expensive Rolex ever

An exceptionally rare and unique Rolex watch just became the most expensive ever sold.

Known as the "Bao Dai" watch, this piece was sold to the last emperor of the Nguyen dynasty in Vietnam in 1954.

Bao Dai Watch

It just sold for over $5 million at auction at Phillips in Geneva. The buyer has not been identified

The Bao Dai is a Rolex reference 6062 — the most expensive and rarest watch model the brand sold at the time it was made. The gold case and black dial were the rarest configuration of the 6062 model.

Only three models to this specification are known to have existed, according to Hodinkee. This particular model is the only one to have had diamond markers on the even hours, making it completely unique and unlike every other watch in the world.

It was sold by the Nguyen family for $235,000 in 2002, meaning that the watch has only changed hands once. Though that price may seem low compared to today's standards, it was also the most expensive Rolex ever sold at the time.

While the watch's auction estimate was only $1.5 million, collectors expected it to go for much more than that. 

The Bao Dai handily beat the previous record holder, the Rolex split-seconds chronograph reference 4113, which sold for $2.5 million last year.