The Armenian Church had split in its doctrine from the Roman Church after the Council of Chlcedon in 451 over monophysitism. At Chalcedon it was affirmed that, in the person of Jesus, there were two distinct aspects, both the human and the divine. Armeni embraced monophysitism, declaring that Jesus was wholly divine.
The two Churches remained in communication, however. Grigor, for instance, participated in a council at Antioch presided over by the papal legate Alberic of Ostia in November 1139. Grigor accompanied Alberic on a pilgrimage to Jerusalem where, in April 1141, he attended a synod at the Templum Domini ("Temple of the Lord") at the Dome of the Rock. While there he vowed to reconcile the Armenian Church with Rome. Alberic reported this to Pope Innocent, who sent Grigor a letter and a pallium, conferring on Grigor a high rank.
With travel to the East becoming common due to the Crusades, envoys from Rome followed along and went to Armenia, continuing dialogue. According to the Armenian Church's own website:
Pontifical Envoys from Rome established continuous contact with the clergy of the Armenian Church, who were hoping to receive political and economic support from the Pope and the Western powers for the Armenian Kingdom. During this period, the Armenian Church adopted some Catholic Church ritual traditions, and Western culture left a tangible trace on Armenian science, art, miniature painting, literature, as well as in various spheres of public life. [source]
The "political and economic support" would have been helpful against enemies both foreign and domestic. Not only were there foreign invaders to contend with, but also the Armenian government could be a problem. The secular ruler of Armenia in 1037, King Hovhannes-Smbat, deposed the Catholicos Petros and appointed a replacement (we'll call him an "anti-catholics," since there were "anti-popes"). The rest of the clergy were so overt in their condemnation that Petros was re-instated.
By the 14th century, a reconciliation between the two entities had been firmly established, and doctrinal differences were being overlooked in order to maintain healthy relations. (The Second Vatican Council in 1962 - 1965 confirmed the reconciliation.)
The Dome of the Rock has been a important site for many groups over the centuries; next time, let's talk about the place and the temple there.