[syn: by chance, accidentally, circumstantially, unexpectedly]
The Collaborative International Dictionary of English v.0.48:
Unexpected \Un`ex*pect"ed\, a.
   Not expected; coming without warning; sudden. --
   Un`ex*pect"ed*ly, adv. -- Un`ex*pect"ed*ness, n.
   [1913 Webster]
WordNet (r) 3.0 (2006):
unexpectedly
    adv 1: in a way that was not expected; "her brother showed up at
           the wedding out of the blue" [syn: unexpectedly, out
           of the blue]
    2: without advance planning; "they met accidentally" [syn: by
       chance, accidentally, circumstantially, unexpectedly]
       [ant: advisedly, by choice, by design, deliberately,
       designedly, intentionally, on purpose, purposely]