Hughie Fury was beaten on a unanimous points decision by Bulgarian Kubrat Pulev in his IBF heavyweight eliminator in Sofia.
All three judges scored the fight in favour of 37-year-old Pulev, who now becomes the mandatory IBF challenger to Anthony Joshua.
Fury, the 24-year-old cousin of Tyson Fury, came into the fight with a 21-1 record - his only loss coming against Joseph Parker in Manchester last September.
Fury sustained a bad cut above his left eye in only the second round and, although he rocked Pulev with a big right hand in the eighth, the Bulgarian came out well on top, with one judge scoring the fight 118-110.