An elusive Rolex triple calendar with moonphase in 18K yellow gold, which belong to the last emperor of Vietnam, is on the auction block again next month. Widely expected to create a new record, the watch was owned by Emperor Bao Dai and is up for grabs at auction house Philips’s Geneva auction on May 13-14 this year.

Considered one of the most valuable Rolexes ever made, this timepiece is only one of three Ref. 6062 produced with a black dial. Further more, of the three black dials, only the Bao Dai-owned 6062 has diamond markers, making it a truly collectible and unique Rolex.

So not only this Rolex a rare and iconic model but it also has imperial provenance, having belonged to the last emperor of Vietnam. No surprise that it has a pre-sale estimate of $1.5 million