Republican Bush had opposed gay marriage while in office, which led some to criticise DeGeneres, an openly gay liberal, for befriending him.
On Monday, during a taping of her television show, DeGeneres said: "I'm friends with George Bush.
"I'm friends with a lot of people who don't share the same beliefs I have."
Bush, who served two terms as US president, has also faced condemnation for leading the country into war with Iraq and Afghanistan.
DeGeneres interviewed Bush on her chat show in 2017.