A Manhattan real estate agent wants answers from his gallerista step-sister on why she hawked a family-owned painting by a renowned abstract artist last year for a measly $375,000 when it re-sold months later for millions.

Cyrus Greenspon claims in court papers that her step-sister's mega-cheap sell-off of their late dad's Ad Reinhardt painting was shady and a conflict of interest — namely because she got her former boss, the president of swanky Pace Gallery, to vouch for its low value and had a friend and former colleague buy it.