Gifford, 66, had lunch with Philbin and his wife, Joy, at Gifford's Connecticut home, where they all shared some laughs together one last time.
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"I was just so grateful the Lord gave me that final time," Gifford said on TODAY Monday. "And it was so precious because when I talked to Joy the day that I found out right after he had passed, she said, 'Kathie he hadn't laughed in a long, long time.' She said, 'I was so worried about him.'
"I think he was like Frank. He was just ready, you know? ... And she said, 'The day that we came to have lunch with you was the last time I heard him laugh.' That will forever be a precious gift the Lord gave me, that I got to laugh again with one of my best friends in all my lifetime."
Gifford said she noticed a difference in Philbin as soon as he got out of the car.
"I sensed much more fragility than I'd seen in him since the last time in January out in Los Angeles," she said. "We sat right here on my screened porch, and we laughed ourselves sick. We always picked up right where we left off. ... After they left I just thought to myself, 'Lord, is that the last time I'm going to see my friend?' Because he was failing, I could tell.
"I don't know, something told me the other day, when I was in Tennessee, 'Get on a plane, and go home. Get on a plane.' And I didn't know why, but I've learned to listen to that voice. I got on the plane, came home and immediately heard the news about Regis, called Joy immediately and talked with her."
Philbin, who died at 88 on July 24, made millions of people laugh alongside Gifford when they co-hosted “Live! with Regis and Kathie Lee” from 1985 until 2000, becoming known for their spontaneous banter and finishing one another's sentences.
Their unscripted conversations and off-the-cuff comedy were the essence of the show.
"When we first started, we had no idea what we had, but we knew what we didn't want," Gifford said. "We didn't want writers, we didn't want a million producers, we didn't want it overproduced. We just wanted to sit there and have fun together.
"We never talked before the show. We didn't have what they call 'elements' in our business. He'd hold up the newspaper, and we're off to the races. Or I'd say, (my son) Cody threw up, and we were off to the races. We never planned it."
The two also built a deep friendship during their time together. Gifford said she had "many, many conversations" with Philbin over the years about faith and what happens after death.
"I know where Regis is, and I know who he's with," she said. "He was very curious, as always, listened. We always respected each other's opinions so highly. You know, in all the years we were together, we never had one cross word."
Their chemistry was evident shortly after they were first paired together on television.
"He was an entertainer in his guts, and so was I, and so when we came together, although we didn't have a friendship yet, we had a mutual respect for what we had accomplished already in our careers," Gifford said. "And we had the same sense of humor, and I wasn't afraid of him, and he sure as heck was not afraid of me, and we just took off like a rocket."
Philbin's irrepressible joy became one of his defining characteristics on and off the TV screen.
"He was the most grateful person in the world," Gifford said. "He never forgot where he came from, and he worked from the bottom up. ... He was just happy to be on a set.
"He just was always comfortable in his own skin and always felt like the luckiest guy in the world."
When asked what she'd miss most about Philbin, Gifford said, "Everything."
"He and Frank had such a great relationship," she said. "There weren’t too many men that Frank could relate to on the same level who had accomplished as much in his own industry and was also beloved and iconic and legendary.
"Frank still had a good head of hair, and so did Regis, and they could let their hair down with one another. So we were blessed not only to be great friends … with Joy and Frank, we were great couples friends. And that’s rare.”
When asked what it was like to sit next to Philbin, Gifford said: "For me, it was the most comfortable place in the world, except sitting next to my husband. Sometimes, Frank said, ‘You spend more time with him than you do with me.’"
Ahead of her look back on TODAY, Gifford also paid tribute to Philbin on Instagram following his death.
"There are no words to fully express the love I have for my precious friend, Regis," the former co-host of TODAY's fourth hour wrote. "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 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."
Tributes to Philbin also poured in from celebrities who sat on the couch to be interviewed by him or worked alongside him.
Gifford and Philbin remained close after she left the show, with Philbin often popping up as a guest on the fourth hour of TODAY after Gifford returned to television in 2008.
Last April, Philbin surprised Gifford with a heartfelt message on her final day at TODAY after she had previously announced she was leaving the show.
"Kathie Lee, you want to know the best part of my life, my TV life, was in the 15 years I spent with you from 1985 to 2000," he said. "We stayed friends through the entire game, and it was a lot of fun. Where you are right now I know you’re going to be moving on to a great new career making movies, and since I’ve seen the first one, I know you’re going to be a great success. I really mean it."