The perfect 1-factorization conjecture for complete graphs

Let $K_{2n}$ be the complete graph on $2n$ vertices. A 1-factorization is a decomposition of its edges into perfect matchings, and it is perfect when the union of any two distinct 1-factors is a Hamiltonian cycle. The perfect 1-factorization conjecture. Every complete graph $K_{2n}$ with an even number of vertices admits a perfect 1-factorization. The conjecture is a strengthening of ordinary 1-factorization for complete graphs; the source attributes it to Ko and does not state whether it has been resolved.