The royals visited the set of The Last Jedi in April 2016 and were rumoured to have filmed a scene in disguise.
Now Boyega, who plays reformed stormtrooper Finn, has confirmed that he shared a scene with the pair "wrapped in stormtroopers costumes".
The actor also appeared to confirm that actor Tom Hardy appears beside them, also beneath a face-obscuring helmet.
Boyega's confirmation came during a taping of a "round table" interview for the Hollywood Reporter. The film website has reported his quotes but has yet to make the audio available. (s:bbc.com)