View Source ExGram.Model.ReplyKeyboardRemove (ex_gram v0.53.0)
Upon receiving a message with this object, Telegram clients will remove the current custom keyboard and display the default letter-keyboard. By default, custom keyboards are displayed until a new keyboard is sent by a bot. An exception is made for one-time keyboards that are hidden immediately after the user presses a button (see ReplyKeyboardMarkup). Not supported in channels and for messages sent on behalf of a Telegram Business account.
Check the documentation of this model in https://core.telegram.org/bots/api#replykeyboardremove