Credit: Craig Barritt/

After calling off her wedding to 85-year-old Hugh Hefner in June, Crystal Harris held onto her estimated $90,000 engagement ring.

But now that several months have passed, the 3.39 carat circular-cut diamond will be auctioned off at Christie's in New York City in October. The former Playboy model, 25, "couldn't bear to look at the ring anymore because it brought back bad memories," a source tells TMZ.

According to the listing, the ring is expected to fetch between $20,000 and $30,000.

Tell Us: Would you bid on Crystal Harris' engagement ring?