The country's champions claim the under-21 international has signed a three-year contract with an option for a further two years.

Mihaylov - 19 on Thursday - told Bulgarian sports website www.sportal.bg after passing a medical: "I have no words - this is the greatest moment of my life."

The goalkeeper, who made his senior international debut in a 5-1 defeat by Scotland in the Kirin Cup in Japan last May, is the son of Bulgarian soccer federation chairman Borislav.