Constantine Tih ya hau gadon sarautar Bulgaria bayan mutuwar Michael II Asen, amma yanayin hawansa ba a sani ba.An kashe Michael Asen da ɗan uwansa Kaliman a ƙarshen 1256 ko farkon 1257. Ba da daɗewa ba, Kaliman ma an kashe shi, kuma dangin maza na daular Asen sun mutu.Rostislav Mikhailovich, Duke na Macsó (wanda shi ne Michael da surukin Kaliman), da kuma boyar Mitso (wanda shi ne surukin Michael), sun yi iƙirarin zuwa Bulgaria .Rostislav ya kama Vidin, Mitso ya mamaye kudu maso gabashin Bulgaria, amma babu ɗayansu da zai iya samun goyon bayan boyar da ke kula da Tarnovo.A karshen ya miƙa kursiyin Constantine wanda ya yarda da zaben.Constantine ya saki matarsa ​​ta farko, kuma ya auri Irene Doukaina Laskarina a shekara ta 1258. Irene diya ce ga Theodore II Laskaris, Sarkin Nicaea, da Elena na Bulgaria, 'yar Ivan Asen II na Bulgaria.Aure tare da zuriyar gidan sarautar Bulgaria ya ƙarfafa matsayinsa.Daga nan aka kira shi Konstantin Asen.Har ila yau, auren ya kulla yarjejeniya tsakanin Bulgaria da Nicaea, wanda aka tabbatar da shekaru ɗaya ko biyu bayan haka, lokacin da masanin tarihin Byzantine da jami'in George Akropolites suka zo Tarnovo.