Chapter 61 of Vishnu Parva, Harivamsa speaks about Rukmi's death.
And verse 55 says
tasminhate mahAvIrye nR^ipatau bhIShmakAtmaje | drumabhArgavatulye vai drumabhArgavashikShite ||
As the great valiant king, the son of bhIShmaka, equal to druma and bhArgava(rAma) and trained by druma and bhArgava(rAma), was killed
Druma, as discussed in my question here had given Vijaya bow to Rukmi. However this question is on Lord Parashurama. If not mistaken he had taken a vow to not train kshatriyas. So how come he had accepted Rukmi as a student ? What's the story behind it ?