In May 774, the Byzantine Emperor Constantine V Kopronymos embarked on a major expedition against Bulgaria, leading his field army on land, and dispatching a fleet of two thousand ships carrying horsemen towards the Danube delta. The fleet disembarked in the vicinity of Varna, but the emperor did not press his potential advantage and inexplicably retreated. Shortly afterwards the two sides signed a truce promising the cessation of hostilities.
However, in October 774 Telerig sent an army of twelve thousand men to raid Berzitia, Macedonia and to transfer its population to Bulgaria.
The subsequent attack on Bulgaria failed, because the imperial fleet encountered contrary winds in the Black Sea. At this point Telerig sent a secret emissary to Constantine V, indicating his intention to flee Bulgaria and seek refuge with the emperor, and seeking assurances of hospitality and a list of Byzantine people who might help him.
Telerig succeeded in having the emperor betray his own agents in Bulgaria, who were duly rounded up and executed. The expected Byzantine retaliation failed to materialize as Constantine V died in 775.
In spite of his apparent success, Telerig found it necessary to flee to the new Byzantine emperor, Leo IV the Khazar in 777.
The Byzantine government gave Telerig asylum and the title of patrikios. The 17th century Volga Bulgar compilation Ja"far Tarikh (a work of disputed authenticity) represents Dilyarek (ie, Telerig) as the son of the former ruler Teles (ie, Telets). Telerig Nunatak on Greenwich Island in the South Shetland Islands, Antarctica is named after Telerig of Bulgaria.