42MM Ballon Bleu WSBB0048 (2023) Pre-Owned CartierThe Cartier Ballon Bleu de Cartier is a 42mm stainless steel watch from Cartier's iconic Ballon Bleu collection, introduced in 2007 and defined by its rounded, double convex case that curves both vertically and horizontally. The Ballon Bleu 33mm (Ref. W6920071) is famously known as the "Kate Middleton" model and remains highly sought after for its timeless steel design. For high end collectors, however, the most desirable pieces are complex references