After the meeting between Sir Galahad and the queen, the book goes on to say that the king and all the estates went home to Camelot, and that as they sat at Supper, the Holy Grail appeared.

Tennyson relates the vision almost in Malory’s own words.

Sir Perceval, having retired from the world, tells the monk, Ambrosius, the history of the quest: 

“And all at once, as there we sat, we heard
A cracking and a riving of the roofs,
And rending, and a blast, and overhead
Thunder, and in the thunder was a cry. 
And in the blast there smote along the hall
A beam of light seven times more clear than day
And down the long beam stole the Holy Grail,
All over covered with a luminous cloud,
And none might see who bare it, and it past. 
But every knight beheld his fellow’s face. 
As in a glory, and all the knights arose,
And staring each at other like dumb men
Stood, till I found a voice and sware a vow. 
I sware a vow before them all that I,
Because I had not seen the Grail would ride
A twelvemonth and a day in quest of it,
Until I found and saw it, as the nun
My sister saw it; and Galahad sware the vow,
And good Sir Bors, our Lancelot’s cousin sware,
And Lancelot sware, and many among the knights,
And Gawayn sware, and louder than the rest.”

It was, in fact, Sir Gawayn who spoke first: 

“Certainly [said he] “we ought greatly to thank our Lord Jesu Christ, for that he hath shewed us this day of what meats and drinks we thought on, but one thing beguiled us, we might not see the Holy Grail, it was so preciously covered.  Wherefore I will make here a vow, that to-morrow, without any longer abiding, I shall labour in the quest of the Sancgreall, that I shall hold me out a twelvemonths and a day, and more if need be, and never shall I return again unto the court, till I have seen it more openly than it hath been seen here.”  When they of the Round Table heard Sir Gawayn say so, they arose, the most part of them, and avowed the same.

As the knights rode out of Camelot to begin their quest there was weeping of the rich and of the poor at their departure.  “The queen made great moan and wailing, and the king might not speak for weeping.”  After some adventures Sir Perceval comes to a chapel to hear Mass, and there he sees a sick king lying on a couch behind the altar; and he was covered with wounds: 

“Then he left his looking and heard his service, and when it came to the sacring, he that lay within the perclose dressed him up and uncovered his head.  And then him beseemed a passing old man, and he had a crown of gold on his head, and ever he held up his hands and said on high:  Fair, sweet father, Jesu Christ, forget not me.  And so he laid him down.  But always he was in his prayers and orisons.  And when the Mass was done, the priest took our Lord’s body and bare it unto the sick king.  And when he had received it he did off his crown, and he commanded the crown to be set on the altar.”