From Hull AWE
'To know' is an irregular verb. Its forms are given here:
|Base form||past tense||-ed participle||Remarks|
- This is one of the "the 250 or so irregular verbs" listed in Quirk 1985. The list "contains most of the irregular verbs in present-day English ... but is not meant to be exhaustive, particularly with regard to derivative verbs." AWE has copied most of the entries in that list. The verb 'to know' belongs to Quirk's Class 4 B a.