Howard Smith was often worried about his friend and neighbor, Johnny Carson."He smoked a lot - he would smoke three packs of cigarettes a day," Smith told Fox News Digital. "He would come over to my house, and wed play tennis, and then after that he would light up a cigarette.""I was probably on him for six months just saying, John, you should consider maybe not smoking as much,'" Smith shared. "One day, he finally told me, Ive realized that its not good for you and I shouldnt be doing it. He never smoked after that."'I LOVE LUCY' STAR DESI ARNAZ BEAT ALCOHOLISM WITH HELP FROM HIS SON: 'I DON'T WANT TO DIE'For the last 18 years of his life, the legendary "Tonight Show" host didnt smoke, Smith claimed in his book. But irrevocable damage was done. In 2002, he was diagnosed with emphysema, a disease that killed him in 2005 at the age of 79.Smith, who "knew and loved" the fiercely private TV icon, has recently written a memoir, "My Friend Johnny: The Last 20 Years of a Beautiful Life with Johnny Carson and Friends." The foreword was written by Jay Leno.WATCH: JAY LENO SAYS HES VERY LUCKY IN LIFE AS HE CARES FOR HIS WIFE WITH DEMENTIA"I wanted people to know John the John I knew," the retired businessman explained. "I was not in show business. I had the largest software company in the world at that time. And I think because I wasnt in show business, he could trust me. And in showbiz, you sometimes dont know who you can trust. I think that meant a lot to him.""I have read several things that have been written about John, and I would say that 90% of those articles were not favorable," he shared. "They were down on John. And that was not the John I knew. I wanted people to get to know my friend."And like any good pal, Smith was concerned about Carsons habits. According to his book, Carson was "an avid smoker," prompting him to ask, beg, and even challenge him to consider quitting smoking. And it was Carson's fourth wife, Alexis Maas, who ultimately got him to quit, said Smith."John was a stubborn person," Smith admitted. "Id give him st a lot. I think thats why he liked me, because wed go back and forth on different things. I never treated him like a star."In 2002, CBS News published a story titled "Johnny Carson: I'm Not That Sick." At the time, Carson said through a spokesperson that when it came to his illness, "Im dealing with it the best I can, and it is not causing me any major problems." However, Smith claimed that Carson was a lot sicker than the headline implied. He just didnt want the public "to make a fuss.""In our 20 years of playing tennis together, I knew the sound of Johns laugh, his forehand grunts, and his labored breathing," Smith wrote. "Toward the end, his breathing became increasingly difficult. We started playing less often, and then, sadly, even suddenly, despite all the signs, the day I dreaded arrived."CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTERSmith told Fox News Digital he still vividly remembers the last time he saw his friend. It was after New Years in 2005. He described their evening as "the last supper.""Im at a pharmacy in Malibu, and he happened to be there," Smith recalled. "He goes, What are you doing tonight?' I said, Nothing. He said, Why dont we go get dinner tonight? John's wife had a place in Pittsburgh, so she spent a lot of time with her family there. So, he was by himself on that day. I remember he picked me and my wife up, and we went to this restaurant. We were the first people there and the last to leave.""John was the funniest Ive ever seen him," Smith reflected. "He went on and on, told stories about different people that he had on the show We just laughed so hard. Our stomachs were sore from laughing At one point, I said, I got to go to bed, and John was like, Oh no, Howard, I want to tell you this other story. And it kept going.""Looking back, there must have been something going on in his head that night. We probably had 500 dinners together, and he was never that funny, going on and on. We would have dinner at 6 oclock and be back home by eight.""For some reason, that night, he just wanted to tell us all these stories and make us laugh," Smith continued. "Weve never laughed like that before. It's like he didn't want us to leave without hearing him first. At the end of the night, he drives us up to our house, gets out of the car. He gave both my wife Jane and me a kiss and a hug. Then he tells us, I love you. John was not standoffish, but I'd never seen him do anything like that.""I think he knew he was dying, but didnt want us to worry," said Smith quietly, fighting back tears. "But at that moment, he just wanted to remember the good times. He wanted to tell us how much we meant to him. He wanted to give us the best of himself."According to Smith, Carson died 16 days later.CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER"When I think about that night, I feel he wanted to tell us that he would be OK, and that he loved us," said Smith. "Thats the John I knew."Today, Smith prefers to remember the happier times. While Carson was "intimate and shy," he slowly opened up to his neighbor, who offered to play tennis with him."We used to play tennis three to four days a week," Smith chuckled. "Then one day he said, Howard, I dont think I can play anymore. I think I ran out of gas. But lets do this. On Saturdays and Sundays, you come over to my house. Ill make you a coffee, and well just sit around, talk about life."And in those later years, Carson wasnt craving the spotlight, Smith insisted."After he retired, he had another life," Smith explained. "He was traveling around the world. He went to Africa. He spent two months learning Swahili. Then he went to Russia and learned Russian so he could talk to people there. He would use this telescope at his house to look up at the stars. My wife and I would often have discussions with him about the Big Bang Theory.""A lot of people wished he hadnt retired," said Smith. "But John didnt. He loved being retired. He would study astronomy. He played card tricks. I remember we went to a local restaurant in Malibu for dinner and there was a young kid there doing different card tricks for people. And John was delighted. He would go, Can you do this? He did all kinds of card tricks for this kid John was shy and quiet, but he loved just being himself."And Carson was a loyal friend who didnt think twice about offering a helping hand in secret, said Smith. He quietly donated to the Childrens Hospital in Los Angeles, as well as to a local group dedicated to helping homeless veterans, among other charities."He loved life," said Smith. "And he gave back. He didnt need the publicity for it."Today, Smith wants the public to discover a new side of "the king of late night.""I didnt realize that he and I were building this special bond," said Smith. "But Im still grateful for that day when we first decided to play tennis together."