1,373. One Who Didn't Mourn Before Yom Tov
220:2 If the bereaved did not mourn before yom tov, whether accidentally or on purpose, or if the deceased was buried close to dark so that the surviving relative was unable to do so, then yom tov doesn't cancel shiva. This case is treated like one who buries a relative on yom tov.
220:3 If any of the days of shiva other than the seventh fell on erev yom tov, some authorities permit the mourner to launder his clothes, but not to wear them until night, since yom tov cancels the shiva. It's advisable to make sure not to launder them until the afternoon so that it will be obvious that he is doing so for the sake of the holiday. The mourner may not wash (himself) until the night, though some authorities permit washing after mincha close to dark; one should follow the accepted local practice. All authorities agrees that shaving is still prohibited.