FB 851 then QR 4 at Heathrow
Sofia → London → Doha
Timetable, London time
16:55FB 851 from Sofia at the gate
14:15QR 4 to Doha leaves the gate
21 h 20 apart on the timetable, overnight
QR 4 leaves 21 h 20 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.