He had to deal with the death of his father in December, and that came after he had worked his way back from an undiagnosed illness in September that caused him to lose weight and miss five of Tennessee's first seven games. When he wasn't dealing with those issues off the field, he was often in the lineup and playing well at right tackle in place of Jack Conklin, who started just nine games in 2018.
It added up to a challenging season for Kelly, who impressed teammates and coaches with his professionalism.
There were early indications that 2018 wouldn't be just another season for Kelly. He opened the season as a replacement for Conklin in the season opener in Miami, a brutal game that lasted seven hours and 10 minutes because of weather delays, making it the longest in NFL history.
Kelly's problems started when he was hospitalized during the days leading up to Tennessee's Week 2 matchup against the Houston Texans. Tests proved inconclusive, so the nerve-wracking affliction was never identified.
"Literally, we don't know anything," Kelly said after leaving the hospital. "That's kind of the mystery."
Once Kelly, listed at 6-foot-8 and 321 pounds, started to feel better, managing the workload to put weight back on was difficult. He had to be careful not to overwork himself for fear of triggering the illness again, and he didn't return to the lineup until getting five snaps in the Titans' Week 7 game in London against the Los Angeles Chargers.
When Conklin suffered a concussion against the Dallas Cowboys in November, it opened the door again for Kelly to start -- this time against the New England Patriots in Week 10. The Titans played arguably their best game of the season -- a 34-10 win at Nissan Stadium -- and quarterback Marcus Mariota was sacked only twice, thanks in large part to the protection from Kelly and the offensive line.
Losing his dad
The mysterious illness was behind him, but Kelly's world was turned upside down again when he was excused from the Titans' facility on Dec. 10 to go back to the Chicago area to bury his father.
The Titans placed Conklin on injured reserve later that same week with a knee injury, and remarkably, Kelly returned in time to practice two days after his father's burial. He once again was called upon to start at right tackle against the New York Giants in Week 15, and his inner strength to do so didn't go unnoticed by teammates.
"I'm really proud of him," left tackle Taylor Lewan said. "Given the situation he had to deal with before the game, it's hard to even put myself in those shoes. It'd be tough. But he played a great game."
One of the greatest things about football is how much of an escape it is for players and fans, and it proved to be the perfect remedy for Kelly while he was mourning.
"Dealing with everything going on in my personal life was hard," Kelly said after the Titans' 17-0 win Dec. 16 in New York. "Then knowing that the team was relying on me and having to try and catch up was a lot. The whole process of football ... the routine and all the structure of it, in general, helped keep my mind off it. But the game, especially, helped."
Ready for starting role?
Kelly went on to start the next two games to close out the season and his play was strong enough to warrant consideration for a starting spot in 2019. Whether that comes at right tackle or by bumping inside to guard remains to be seen.
In his first year as Titans general manager, Jon Robinson received excellent return after trading a sour 2015 second-round pick (wide receiver Dorial Green-Beckham) to the Philadelphia Eagles for Kelly, a player who has starting-caliber talent and is a true example of how to be a professional.
"I've said several times, Dennis could be a starting tackle in this league, no problem," Lewan said. "We're extremely lucky to have him. I can't say enough good things about Dennis, man. I remember someone said in a meeting one time that Dennis is the true meaning of a pro. He's the best pro I've seen. He comes in every single day and works. And every time he's been called upon, he's excelled."
Little did Robinson know he was acquiring a player as devoted as Kelly. The way he fought through his hurdles last season proved it.
Now the Titans have to figure out how to get him on the field more.