fortuitous

adjective3

1. •
   Happening by fortune or chance; accidental, coincidental.

   • [D]uring the ten days of their stay at Hartfield it was not to be expected—she did not herself expect—that any thing beyond occasional, fortuitous assistance could be afforded by her to the lovers. — 1815
2. •
   Happening by good fortune or success; fortunate, lucky.

   • And then he met John Dowsett, the great John Dowsett. The whole thing was fortuitous. This cannot be doubted. — 1910
3. •
   Happening independently of human control; uncontrollable.