It's the book she wishes she didn't have the details to write, the story she wishes she'd never lived through. Yet, Erin Kelly is sharing the story of her father's fight against cancer and what it has taught her – and can teach the world – of the true meaning of the words she grew up hearing – "Kelly Tough."

Erin's father, Jim Kelly, is the most beloved quarterback – and likely player - in the history of the Buffalo Bills. The strong-armed quarterback who was never afraid to take a hit led the Bills to four consecutive Super Bowls appearances from 1990-1993; the Bills lost all four. In his first Super Bowl appearance, XXV, he led a two-minute drill into field goal range only to watch Scott Norwood's 47-yard attempt famously sail "wide right."

Larence Taylor pressures Jim KellyHis commitment and dedication to the game were never questioned, even in the face of great disappointment. His perseverance stood true with his family motto, to be "Kelly Tough." The quarterback with a "linebacker's mentality" still holds almost every one of the Bills' all-time records in passing stats, although not games played or career interceptions. 

The Pro Football Hall of Famer had his life drastically change when he was diagnosed with upper jaw cancer in early June of 2013. He underwent surgery to remove part of his jawbone within weeks of his diagnosis and was then declared cancer free. The brief scare for his family was over.

That is, until March 14, 2014. Just under a year after his initial diagnosis, Kelly was informed his cancer had returned. Erin Kelly and her mother, Jill, were on the other side of the world, in Israel, when they received news. It was then the once invincible star started on the hardest five-and-a-half month journey of his life - ironically almost the exact length of time from Week 1 of the NFL season to the Super Bowl.

Throughout his battle, his wife, Jill, and his daughters, Erin and Camryn, were by his side. One day, after visiting her father in the hospital, Erin made a journal entry on what the phrase "Kelly Tough" truly meant to her. She gave the entry to her father, who took great pride in her work, and it was then she began penning a full length book, with her mother, Jill, on her father's - and her family's - battle.Kelly Tough

"He shared (the journal entry) with anyone who would come into his hospital room and it went from there," Erin explained to TSN.ca of her 'Kelly Tough' entry. "He was very supportive of the whole thing, knowing the deeper meaning of ('Kelly Tough') – that it could encourage someone else. "

Erin's story, "Kelly Tough: Live Courageously by Faith" goes far beyond Jim's battle. As she writes, there were good days and bad days as her father's battle raged, but they went far beyond the fight in his body itself.

For Erin, there was facing strangers on Twitter declaring their wishes for her father's death and the longing feeling to be involved while away at University. There was also the pain that resurfaced from the Kelly family's last struggle, the life – and death – of Jim and Jill's first, and only, son Hunter.

"Through 'Kelly Tough,' I was reliving every moment and I was chronicling what happened not only with my brother, Hunter, when he was going through his disease," Erin explained. "But my dad and what he was going through with cancer and everything in between – moments in my life that have really taught me what it means to be "Kelly Tough"."

Just months after her younger brother Hunter's birth in 1997, he was given three years to live by doctors after being diagnosed with Krabbe Disease. Hunter lived to the age of eight, passing away on August 8, 2005 – the worst day of Erin's life.

"Having to relive those moments in my life was hard for me," Erin recalled. "To not know how much to share, or what to share, with really the world and anyone who ever wants to read it about my life. So, it was hard but at the same time it was really rewarding to see what God did in the midst of it."

When Jim Kelly found out he would be a member of 2002 Pro Football Hall of Fame induction class, he began to pray Hunter, then five, would be there to watch him at the ceremony six months away.

Jim Kelly at Pro Football Hall of Fame enshrinement"God has granted me that blessing," Kelly told the crowd in Canton, Ohio at his induction ceremony. "It has been written throughout my career that toughness is my trademark. Well, the toughest person I've ever met in my life is my hero, my soldier, my son, Hunter. I love you, buddy."

That speech marked the first time Erin, then seven years old, had ever heard the idea of being "Kelly Tough" – the expression that would come to mean so much to her, her family and so many beyond.

Those words, and her story, she hopes will continue to inspire those faced seemingly insurmountable odds.

"Ultimately my heart in writing 'Kelly Tough' was to encourage people to live courageously and fearlessly in faith," Erin said. "We all have our own stories, we all have our own circumstances where we need to be tough and so, [my goal] was to hopefully encourage someone else."

Even as she stood confident in her faith and father's renowned toughness, Erin knew there was no promise of a happy ending to her story.

"There was definitely fear along the way," Erin said honestly. "Knowing that, I might not have my father to walk me down the aisle one day - those were hard moments for me.

"Knowing that, OK, I'm writing this story when we don't know (how it will end). My mom and I were just going back and forth during the whole writing process, knowing that we don't know what the outcome of this will be. It was really writing by faith."

Erin, 20-years-old, says her definition of "Kelly Tough" changed greatly as she watched Jim's fight for his life through months of treatment and, at times, needing a feeding tube to survive.

"He drilled (the phrase) into us from a very young age because that's how he grew up," said Erin. "His dad grew up telling him and his five brothers to be 'Kelly Tough.' It was; when you fell down on the basketball court, 'you're ok, get up, be 'Kelly Tough.' I didn't really know the fullness of what that meant until I actually saw my dad be weak, until I saw him going through cancer and that this 'Kelly Toughness' is not about the Kelly family at all, it's about finding your strength in God in the midst of your own weaknesses."

Jim Kelly won his battle against cancer on September 4, 2014. He then was forced to battle through an MRSA in November, needing a month a fight that off. Erin says her family is deeply grateful for the support they received from around the NFL, and especially in the city of Buffalo during Jim's fight.

 

THANK YOU GOD!!! Jim telling Erin Marie the amazing NEWS!!!

A video posted by Jill Kelly (@jillmkelly) on

"It was very humbling to see Buffalo really rally around the Kelly family," Erin said. "We consider the Buffalo community to be family to us and they've always been that way. To see them rally behind us when my dad was struggling, and people connecting with us saying 'we're praying for you, whatever we can do just let us know,' it definitely helped my dad get through the whole cancer process.

"I would say that the turning point in everything was when he returned to Buffalo, because initially he was getting treatment in New York City and it got to a point where we knew he needed to come home."

 

NYC has been good to us. BUT...there's no place like HOME! No place like Buffalo! #weLOVEyou #prayersforJK #BUFFALO

A photo posted by Jill Kelly (@jillmkelly) on

Jim Kelly received support from his former teammates, opponents, supporters and even opposing fans throughout his battle. The reaction he garnered allows Erin to take great pride in being Jim's daughter.

"It was incredible to see the amount of people from the NFL community that surrounded us, especially his former teammates and even his former opponents," Erin said. "Like, Dan Marino coming to the hospital and seeing him.

"We had Dolphins fans, and Jets fans, and Patriots fans coming and saying 'I hated your dad on the field but we love him now and we're supporting you.' To know that as his daughter makes me proud and so thankful and humbled that people are still surrounding us in prayer."

As for Erin, she still doesn't consider herself a writer despite "Kelly Tough" marking her sixth book. She is currently heading into her junior year at Liberty University, where she studies digital media. A die-hard Bills fan, Erin has received support from Rex Ryan along her book tour and is excited for the upcoming NFL season.

"I never will be a Patriots, or a Dolphins, or a Jets fan," Erin promised, "but we are definitely thankful of those people (who supported us)."

"Kelly Tough" was released on May 1 and is available everywhere books are sold.