This isn't 100% percent correct, but it's very easy to play/follow along to his version 
using these chords. Or even if you want to make your own little version of it that is 
similar to his.

CAPO 3

VERSE

Em F#m G
Em F#m A D
Em F#m G
Em F#m

prechorus- Em C B

CHORUS

G G/F#m
G G/F#m
Em F#m G (C)
Em F#m-

prechorus- Em C B

O Come All Ye Faithful
Joyful and triumphant,
O come ye, O come ye to Bethlehem.
Come and behold Him,
Born the King of Angels;
O come, let us adore Him,
O come, let us adore Him,
O come, let us adore Him,
Christ the Lord.

O Sing, choirs of angels,
Sing in exultation,
Sing all that hear in heaven God's holy word.
Give to our Father glory in the Highest;
O come, let us adore Him,
O come, let us adore Him,
O come, let us adore Him,
Christ the Lord.

All Hail! Lord, we greet Thee,
Born this happy morning,
O Jesus! for evermore be Thy name adored.
Word of the Father, now in flesh appearing;
O come, let us adore Him,
O come, let us adore Him,
O come, let us adore Him,
Christ the Lord.