The family of former NFL wide receiver Demaryius Thomas, who died suddenly on Thursday at age 33, believe they know the cause of their relative’s death.

Five-time Pro Bowl star and 2016 Super Bowl winner Thomas passed away at his Georgia home, with his former team the Denver Broncos in mourning and many ex-colleagues revealing they were “heartbroken” by the news.

READ MORE: NFL icon dead at age 33 after ‘medical issue’

It was originally unknown what had caused the untimely passing, with Roswell police saying “preliminary information is that his death stems from a medical issue, and our investigators currently have no reason to believe otherwise”.

The NFL family mourns the tragic loss of Demaryius Thomas and we extend our deepest condolences to his family and loved ones. pic.twitter.com/rAXYguAUy1

— NFL (@NFL) December 10, 2021

On Friday, however, Thomas’ family shed light on health issues faced by the constantly smiling star, who retired in June this year.

“He had been suffering from seizures for over a year, and we believe he had a seizure when he was showering,” revealed his cousin LaTonya Bonseigneur as per AP.

“We’re not sure when he died. We just spoke with him yesterday.”

Bonseigneur, to whom Thomas was close, said that a friend called his driver when he “couldn’t get a hold of him,” and asked him to check if her cousin was alright.

We are devastated and completely heartbroken.

Demaryius’ humility, warmth, kindness and infectious smile will always be remembered by those who knew him and loved him. pic.twitter.com/0GLZIr6UP3

— Denver Broncos (@Broncos) December 10, 2021

Granted free access to Thomas’ residence by his family due to the seriousness of the seizures he had been suffering, the driver discovered him in the shower.

In spite of this, an official cause of death has still not been set for Thomas, who would have turned 34 around a fortnight from now on Christmas Day.

Also joining fellow GOAT candidate Peyton Manning – who won the Super Bowl alongside Thomas – in tribute to the deceased was another legendary quarterback in Tom Brady. 

“I’m so sad to wake up this morning to hear about the passing of my friend Demaryius Thomas,” said Brady, who played with him at the New England Patriots in 2019. 

Im so sad to wake up this morning to hear about the passing of my friend Demariyus Thomas. We were all blessed with his humility and positive spirit, and we will all miss him. This photo is from the Hall of Fame this past August, a source of light as always. RIP pic.twitter.com/o3hvQN0cRz

— Tom Brady (@TomBrady) December 10, 2021

“We were all blessed with his humility and positive spirit, and we will all miss him. This photo is from the Hall of Fame this past August, a source of light as always. RIP,” Brady finished, referencing a selfie of the pair also uploaded.

Catching his last competitive ball at the New York Jets, Thomas is best remembered for nine impressive seasons at the Broncos where he became their all-time receiving yards in a game (226) and season (1619) record holder as well as the holder of the most touchdown receptions (14).