Abstract: An expanding panel fastener assembly for affixing a honeycomb panel structure to a support structure is disclosing having an insert member that attaches to a hole drilled within the honeycomb panel. A flexible sleeve and retainer assembly includes a molded flexible sleeve, an expander member and a retainer member. A sleeve spacer can further be attached to the flexible sleeve to assist in retaining it within the insert member. By providing a fastener for engagement with the retainer member, the expander member can further prevent withdrawal of the retainer member and can further assist in expanding the flexible sleeve to provide a sealing configuration with any support structure.