Titus of Bostra — as excerpted in the Catena Aurea on Luke 8:19-21

“Our Lord had left His kinsfolk according to the flesh, and was occupied in His Father’s teaching. But when they began to feel His absence, they came unto Him, as it is said, Then came unto him his mother and his brethren. When you hear of our Lord’s brethren you must include also the notions of piety and grace. For no one in regard of His divine nature is the brother of the Saviour, (for He is the Only-begotten,) but He has, by the grace of piety, made us partakers in His flesh and His blood, and He who is by nature God has become our brother.”