On 28 October 2025, the LIGO-Virgo-KAGRA Collaboration announced the discovery of two binary black holes observed during the fourth observing run. Both systems have rapid and precisely-measured spins for the primary (the larger black hole in the pair), have unequal mass ratios, and show spin-orbit misalignment. This suggests that the primary in these two systems was itself formed from an earlier binary coalescence in a dense stellar environment.