[...] "The aforesaid King of Hungary [Géza II] died, leaving as heir a young son, a very little boy [Stephen III] at the time.
Then the king's brother [Ladislaus II] came to Archbishop Luke, demanding from him both installation and coronation.
Luke reproved this man and accused him of treachery for ignoring law and custom and right, in his efforts to disinherit the innocent and he refused to consent.
But the uncle had himself made king by another 
archbishop of the kingdom [Mikó of Kalocsa], who had no authority for such a coronation.
It was as if the usurper had said: »if I cannot move the powers above, I will solicit those of hell« [a quote from Virgil's Aeneid].
He was immediately visited with anathema by Luke, whom he forthwith urged with dreadful threats and even with the menace of a naked sword to absolve him; but, receiving for an answer scorn and like-wise excommunication, he thrust the Archbishop violently into prison and compelled the suspended churches to disregard the interdict."

— Walter Map: De nugis curialium
Géza II died unexpectedly on 31 May 1162.
Archbishop Lucas crowned Géza II's elder son, 15-year-old Stephen III king without delay in early June in Székesfehérvár.
Immediately after the coronation, Byzantine Emperor Manuel, who attempted to extend his influence over the neighboring kingdom, dispatched an army to Hungary which advanced as far as Haram (now Ram, Serbia) and sent envoys to Hungary to promote the claim of the young monarch's namesake uncle to the Hungarian throne.
Most of the lords opposed Stephen as their king because of his familial relationship with Manuel.
The magnates decided to accept Stephen's uncle, Ladislaus II, as a "compromise candidate" between being bribed by the Byzantines and being afraid of a potential invasion by the Emperor.
Stephen III's army was routed at Kapuvár and he fled from Hungary and sought refuge in Austria six weeks after his coronation.

Archbishop Lucas stayed in Hungary after the Byzantine intervention and was one of the few who remained loyal to Stephen and refused to crown Ladislaus; as a result, Mikó, Archbishop of Kalocsa performed the ceremony in July 1162, despite the coronation of the Hungarian monarch being the Archbishop of Esztergom's responsibility for centuries.
Lucas considered Ladislaus II to be an usurper and excommunicated him through his envoy, declaring that he had unlawfully seized the crown from his nephew.
Lucas also excommunicated his fellow archbishop Mikó for his participation in the process.
As Makk noted, the legal basis for Lucas to impose ecclesiastical punishment against Ladislaus II was provided by Article 17 of St. Stephen's Second Code and Article 2 of the so-called Second Synod of Esztergom during the reign of Coloman.
According to Map's De nugis curialium, the new monarch tried to intimidate and persuade the prelate to his side, but Lucas remained steadfast and strongly condemned his controversial accession to the Hungarian throne.
In response the archbishop was arrested and imprisoned shortly thereafter.

"Since Luke's imprisonment long continued, a friend of his brought secretly to him in prison orders for his liberation from Pope Alexander addressed to the king, but these Luke was utterly unwilling to use when he heard that they had cost twelve denari — the 
wonted price for a bull — the good man declaring that he would not be delivered by simony.
But the Lord opened his prison on Easter Day [in fact, Christmas] while the king was at a solemn mass.
Then Luke entered the chapel with all men agape, and, having uncovered the altar and cast aside its ornaments, he thus spoke in the presence of the cross and in the hearing of the king, who was dazed with fear: »O Lord Jesus, whose resurrection no men but Christians proclaim, through that sovereign virtue by which Thou arose from the dead, if Thou deemest this king deserving of Thy visitation, "overthrow the wicked that he be no more" [Prov.
12,7]; but if not, at least let him feel, within forty days in Thy strong right hand which smote Pharaoh, the power of Him whom this marf
[...] "The aforesaid King of Hungary [Géza II] died, leaving as heir a young son, a very little boy [Stephen III] at the time. Then the king's brother [Ladislaus II] came to Archbishop Luke, demanding from him both installation and coronation. Luke reproved this man and accused him of treachery for ignoring law and custom and right, in his efforts to disinherit the innocent and he refused to consent. But the uncle had himself made king by another 
archbishop of the kingdom [Mikó of Kalocsa], who had no authority for such a coronation. It was as if the usurper had said: »if I cannot move the powers above, I will solicit those of hell« [a quote from Virgil's Aeneid]. He was immediately visited with anathema by Luke, whom he forthwith urged with dreadful threats and even with the menace of a naked sword to absolve him; but, receiving for an answer scorn and like-wise excommunication, he thrust the Archbishop violently into prison and compelled the suspended churches to disregard the interdict."
— Walter Map: De nugis curialium
Géza II died unexpectedly on 31 May 1162. Archbishop Lucas crowned Géza II's elder son, 15-year-old Stephen III king without delay in early June in Székesfehérvár. Immediately after the coronation, Byzantine Emperor Manuel, who attempted to extend his influence over the neighboring kingdom, dispatched an army to Hungary which advanced as far as Haram (now Ram, Serbia) and sent envoys to Hungary to promote the claim of the young monarch's namesake uncle to the Hungarian throne. Most of the lords opposed Stephen as their king because of his familial relationship with Manuel. The magnates decided to accept Stephen's uncle, Ladislaus II, as a "compromise candidate" between being bribed by the Byzantines and being afraid of a potential invasion by the Emperor. Stephen III's army was routed at Kapuvár and he fled from Hungary and sought refuge in Austria six weeks after his coronation.
Archbishop Lucas stayed in Hungary after the Byzantine intervention and was one of the few who remained loyal to Stephen and refused to crown Ladislaus; as a result, Mikó, Archbishop of Kalocsa performed the ceremony in July 1162, despite the coronation of the Hungarian monarch being the Archbishop of Esztergom's responsibility for centuries. Lucas considered Ladislaus II to be an usurper and excommunicated him through his envoy, declaring that he had unlawfully seized the crown from his nephew. Lucas also excommunicated his fellow archbishop Mikó for his participation in the process. As Makk noted, the legal basis for Lucas to impose ecclesiastical punishment against Ladislaus II was provided by Article 17 of St. Stephen's Second Code and Article 2 of the so-called Second Synod of Esztergom during the reign of Coloman. According to Map's De nugis curialium, the new monarch tried to intimidate and persuade the prelate to his side, but Lucas remained steadfast and strongly condemned his controversial accession to the Hungarian throne. In response the archbishop was arrested and imprisoned shortly thereafter.
"Since Luke's imprisonment long continued, a friend of his brought secretly to him in prison orders for his liberation from Pope Alexander addressed to the king, but these Luke was utterly unwilling to use when he heard that they had cost twelve denari — the 
wonted price for a bull — the good man declaring that he would not be delivered by simony. But the Lord opened his prison on Easter Day [in fact, Christmas] while the king was at a solemn mass. Then Luke entered the chapel with all men agape, and, having uncovered the altar and cast aside its ornaments, he thus spoke in the presence of the cross and in the hearing of the king, who was dazed with fear: »O Lord Jesus, whose resurrection no men but Christians proclaim, through that sovereign virtue by which Thou arose from the dead, if Thou deemest this king deserving of Thy visitation, "overthrow the wicked that he be no more" [Prov. 12,7]; but if not, at least let him feel, within forty days in Thy strong right hand which smote Pharaoh, the power of Him whom this marf 
Lucas, Archbishop of Esztergom