The famed Mauritius Ball cover franked with the red One Penny "Post Office" stamp is one of just three known and the only one privatly owned. It was hammered down 26 June 26 2021 by the German philatelic auction house of Christoph Gaertner for €8.1 million. With the buyer’s premium of 23.8 percent, that works out to $11.94 million at current exchange rates.
engraved by <a href="https://en.wikipedia.org/wiki/Joseph_Osmond_Barnard" class="extiw" title="w:Joseph Osmond Barnard">Joseph Osmond Barnard</a>
<a rel="nofollow" class="external text" href="https://www.linns.com/images/default-source/news/mauritius-1847-ball-cover-world-record-auction-price.jpg">The cover</a> is linked on <a rel="nofollow" class="external text" href="https://www.linns.com/news/auctions/mauritius-ball-cover-sells-for-almost-%2412-million-an-all-time-record-price">this webpage</a> (Published by <a href="https://en.wikipedia.org/wiki/Linns_Stamp_News" class="extiw" title="w:Linns Stamp News">Linns Stamp News</a> 30 June 2021)