Love triangle in a fantasy novel

The fantasy novel I'm outlining has three major characters: an African queen, a male European barbarian, and a female Asian warlord. The warlord has conquered the queen's country, so the queen runs away to another kingdom to raise an army and bumps into the wandering barbarian. The barbarian and the queen have several adventures along the way and ultimately fall in love, but one of the twists is that the warlord is the barbarian's ex-girlfriend. That makes the barbarian reluctant to help the queen fight the warlord, especially since the breakup wasn't actually a hostile one (it simply involved diverging careers between the barbarian and the warlord).

The question I want to ask is how early in the story should I disclose this twist. Should I have the barbarian bring it up when he and the queen are explaining their backstories after they first meet? Or should I have him keep his relationship with the warlord a secret until later in the story?

I think you should just have the barbarian quickly mention something about a past love when he meets the queen, but not go into detail. Save that it is the warlord until later.

^ That could work. Thank you!