Multiple problems remain with the Standard Model (SM), including the abundance of matter over antimatter in the universe that motivates sources of charge-parity violation (CPV) beyond the SM (BSM). Double-charm B meson decays provide insight into both SM and BSM physics, especially BSM sources of CPV. Recent measurements of these decays with the LHCb detector will be discussed. Firstly, a search for sixteen decays of the Bc meson, which revealed the first evidence for the Bc->Ds+D0bar decay contrary to expectations, will be presented. If confirmed with future datasets, the measured branching fraction would require either a large departure from our understanding of the phenomenology of the Bc meson or a contribution from BSM physics. Secondly, measurements of CPV and branching fractions in the double-charm decays of the lighter B mesons will be presented, including the world-first measurement of several CP asymmetries. Flavour symmetries between these decays constrain subleading amplitudes permitting percent-level sensitivity to potential BSM contributions, and the implications of these measurements will also be discussed.