There were many highlights to choose from – enough platinum to sink a small ship, precious-stone dials, limited editions and even the Royal Oak owned by Genta himself, which capped proceedings with a hammer price of $2.1 million and became the most expensive vintage Royal Oak ever sold in the process. But one other stood out for us: the last lot offered at the Phillips sale on 6 May. Described as “a very distinctive blackened stainless steel wristwatch with date and bracelet” from 1973, it was estimated to fetch between CHF 100,000 and 200,000 (£82,000 and £164,000), but eventually sold for an enormous CHF 937,500 (£771,000).

To look at, it isn’t in particularly good condition, but neither has it attained the kind of magical patina that normally drives collectors wild. The black coating has rubbed away around the bezel, case edges and links, and the tapisserie dial pattern all Royal Oaks are famed for has discoloured unevenly, especially around the hour markers. So why the stratospheric valuation? The clue is in the colour of the watch itself. It was given the unorthodox treatment by its owner, Mr Karl Lagerfeld, in line with his obsession with all things black.

Provenance – auction-speak for “this was owned by someone important or interesting” – is everything in vintage watches and makes the difference between a valuable watch and a priceless one. Being owned by the renowned designer and creative director would be provenance enough, but this particular Royal Oak sparked such interest because Lagerfeld gave it a personal makeover, coating the entire case, bracelet and bezel black. In doing so, he was at the cutting edge of what was possible in the early 1970s (Porsche Design made the first all-black production watch in the same year as the Royal Oak launched, in 1972) and at least 40 years ahead of mainstream watch tastes. Despite the existence of some all-black models, the vogue for customised all-black luxury watches such as the Royal Oak, Nautilus and Rolex sports models, did not land until the mid 2000s and aftermarket customisers such as Pro Hunter, Titan Black and, in its original guise, Bamford Watch Department.

It was a few more years before mainstream brands started to follow suit and Panerai, Hublot, Tudor and Bell & Ross produced their own black designs. Audemars Piguet didn’t release an all-black version of the Royal Oak until 2016, when it had mastered the technology to make its intricate shape in solid ceramic to avoid any chance of a coating – no matter how high quality – wearing off, as Lagerfeld’s early attempt did. There was one other brand that got in on the all-black trend much earlier than others: Lagerfeld’s own Chanel, with the release of the J12 in 2000. Admittedly, watches were the artistic director Mr Jacques Helleu’s department, but can it really be a coincidence? Lagerfeld was, whichever way you look at it, decidedly ahead of his time.