Old English æfterwearde "behind, in back, in the rear," from æft "after" (see aft) + -weard suffix indicating direction (see -ward); expanded by influence of after. Variant afterwards shows adverbial genitive. Old English also had æfterweardnes "posterity."
it didn't happen until afterward
aftermarket
aftermath
afternoon
aftershock
afterthought
afterward
afterwards
afterword
aftward
ag
*ag-