While Gifford, 66, admitted there are simply "no words to fully express" her love for her "precious friend," she called his life "legendary."
"I simply adored him and every day with him was a gift. We spent 15 years together bantering and bickering and laughing ourselves silly — a tradition and a friendship we shared up to this very day. I smile knowing somewhere in Heaven, at this very moment, he's making someone laugh," she wrote.
Gifford's statement continued: "It brings me great comfort knowing that he had a personal relationship with his Lord that brought him great peace. I send all the love in my heart to Joy, to his children, to the rest of his family and to the innumerable people he touched over his legendary life. There has never been anyone like him. And there never will be."
The TV legend died of natural causes, his family announced in a statement shared with Fox News on Saturday.
"We are deeply saddened to share that our beloved Regis Philbin passed away last night of natural causes, one month shy of his 89th birthday," his family said.
"His family and friends are forever grateful for the time we got to spend with him — for his warmth, his legendary sense of humor, and his singular ability to make every day into something worth talking about. We thank his fans and admirers for their incredible support over his 60-year career and ask for privacy as we mourn his loss."
TV personalities Kathy Lee Gifford (L) and Regis Philbin are seen in Midtown on September 23, 2015 in New York City. (Michael Stewart/GC Images)
Philbin and Gifford began their stint on "Live! with Regis and Kathie Lee" in 1985. The co-hosts who captured Americans' hearts with their daily morning banter had a 15-year-run until Gifford left the show in 2000.
“No arguments, no harsh words in all this time,” Philbin said of his experience working alongside Gifford to a theater audience in 2000. “Well, there was the time I didn’t talk to her for two weeks. Didn’t want to interrupt her.”
After a tryout period for a replacement, Kelly Ripa, then best known for her acting in the soap drama “All My Children," filled the slot.
Philbin departed the show in 2011. Although he said Ripa took his exit personally, he explained on "Larry King Now" that his decision was due to him getting older and that it "wasn't right for me anymore."
Despite his lengthy resume and stamina throughout this decades-long career, Philbin did suffer some minor health setbacks. In 1993, doctors performed an angioplasty to relieve a blocked artery. He also underwent bypass surgery in 2007 at age 75.