infinitive

present

stumble across

indicative

present

(I)stumble across
(you)stumble across
(he,she,it)stumbles across
(we)stumble across
(you)stumble across
(they)stumble across

past

(I)stumbled across
(you)stumbled across
(he,she,it)stumbled across
(we)stumbled across
(you)stumbled across
(they)stumbled across

participle

present

stumbling across

past

stumbled across