We got Derek at LAX and the 'DWTS' alum told us Ariana follows the formula for the dancing competition show ... the perfect candidate.
That formula, as Derek explains, loosely goes like this, at least for reality stars ... they get their big break and become household names, then go on 'DWTS' to raise their profile.
Ariana's a textbook example ... she's been dominating headlines since March when she found out her longtime boyfriend Tom Sandoval was cheating on her with their "Vanderpump Rules" costar Raquel Leviss.
Derek says he's been consumed with planning his upcoming wedding rather than paying attention to the Scandoval ... but he knows a good story when he hears one, and he quickly endorses the Ariana move.
There are reports Ariana is already in talks to join 'DWTS' for season 32 ... and Derek's not opposed.