That’s one rock-bottom rock.

Ex-Brooklyn Net Kris Humphries auctioned off Kim Kardashian’s $2 million engagement ring Tuesday — for a paltry $749,000.

Christie’s had listed the 20.5-carat monstrosity as “Impressive Diamond Ring” in its Magnificent Jewels auction.

Humphries has had no use for the behemoth bauble since splitting with Kim in 2011, after 72 days of marriage.