20 But the time will come when the bridegroom will be taken from them, and on that day they will fast.

Read Mark 2:20 Using Other Translations

But the days will come, when the bridegroom shall be taken away from them, and then shall they fast in those days.
The days will come when the bridegroom is taken away from them, and then they will fast in that day.
But someday the groom will be taken away from them, and then they will fast.