Sotheby's said the fees were for "third-party advisory, legal and other professional service fees directly associated with issues related to the shareholder activism and the resulting proxy contest with Third Point and the associated litigation."
Of that amount, $10 million will be paid to Loeb to reimburse him for his expenses.
Manet portrait smashes record at Christie's
Loeb launched a scathing activist campaign against Sotheby's last year, likening the company to an "old master painting in need of restoration" and calling for the ouster of CEO William Ruprecht.
Sotheby's and Loeb reached an agreement in May, with Loeb's Third Point getting three board seats.
Read MoreChinese tycoon paid what for a van Gogh?!
So has the $20 million been worth it?
Loeb has certainly done well, getting reimbursed for his battle and getting three board seats in the deal.