"Let" is one of the "invariable" irregular verbs; its present, past, and past participle are all "let".
The past participle of "let" is "let."
The past tense of "let" is "let." The past participle is also "let."
The past participle of the word "have" is "had."
The past participle is let. The simple past tense is letted.
The past participle of the word "do" is "done."
The past participle of the word "finish" is "finished."
The past participle of the word "pick" is "picked".
The past participle of the word "Find" is the word "Found."
The past participle of the word 'fall' is 'fallen'.
The past participle of the word "swore" is "sworn."
The word "invited" is the past participle of invite.
The past participle for the word "welcome" is "welcomed."