Hull sign Gardner and King
Gardner was already at the KC Stadium on loan, but Tigers manager Phil Brown persuaded the centre-back to a sign a permanent three-year contract.
"We had an option to make the deal permanent at any stage, so I spoke to him and asked him if he would be happy to stay," Brown said.
"He has been at the club for four or five weeks now and he said he would, so he now becomes our record signing."
King, 28, had been discussing a move to Hull for several weeks, and the transfer was finally completed after the Jamaica international passed a medical.
Gardner and King could make their debuts in Saturday's Premier League opener against Fulham.