(CNN)US tennis star Jessica Pegula says her sister, Kelly, saved their mom's life after she went into cardiac arrest at her home last year.
In an article published in The Players' Tribune on Tuesday, Pegula opened up about her family's "tough" year which culminated in "some bizarre, messed-up, full circle moment" when Damar Hamlin suffered a cardiac arrest on the pitch during an NFL game.
In June last year, reports emerged regarding Pegula's mom, Kim -- a co-owner of the NFL's Buffalo Bills and the National Hockey League's Buffalo Sabres -- being hospitalized.
Not much was known about her condition at the time but Pegula, in her recent article, wrote in detail about what happened and how her mom has been recovering ever since.
"My mom was asleep when my dad woke up to her going into cardiac arrest and she was unresponsive for quite a while," Pegula said.
"My sister gave her CPR until the ambulance arrived. She saved her life. Even though she doesn't like to take credit for this terrible situation, she absolutely saved her life, followed by the critical job performed by the paramedics who arrived and were able to restore a heartbeat."
Pegula's mom has been the co-owner of the Bills since 2014, when she purchased the franchise with her husband, Terry, for more than $1 billion.
The pair also own the NHL's Buffalo Sabres, making Kim the first woman to become president of both an NFL and NHL team.
Pegula says her mom loved her work and was very much the engine room of the sporting empire, but she worries that "she won't be able to be that person anymore."
"She is dealing with significant expressive aphasia and significant memory issues," Pegula said. Aphasia is a language disorder caused by damage in a specific area of the brain, according to Johns Hopkins Medicine.
"She can read, write, and understand pretty well, but she has trouble finding the words to respond. It is hard to deal with and it takes a lot of patience to communicate with her, but I thank God every day that we can still communicate with her at all.
"The doctors continue to be blown away by her recovery, considering where she started, and her determination is the driving force of that."
She says the family practically lived at the hospital during the first two weeks of the recovery process, with her father reluctant to go home without his wife.
The pressure of caring for the family and running a successful business empire took its toll on everyone, Pegula says.
"When they say one day in the hospital equals a week to recover, that is no joke. We were all mentally and physically exhausted," she added.