Alex Rodriguez's girlfriend Jaclyn Cordeiro turns up the glamor in sleek black dress at star-studded premiere of Yankees icon's HBO show ft. Tom Brady

Alex Rodriguez's girlfriend, Jaclyn Cordeiro, turned heads at HBO's Alex vs A-Rod premiere on Thursday at 9 p.m. ET/PT. Before the Canadian fitness trainer arrived at the show, she posted a mirror selfie, revealing her outfit for the evening.

Cordeiro wore a black, long-sleeved velvet dress with a deep V-neckline. She complemented the outfit with black open-toed high-heeled sandals with thin straps. She is also carrying a small, black clutch bag, wearing a thin gold necklace with a small pendant and a golden watch.

Alex Rodriguez also posted photos from the evening. He posed alongside seven-time Super Bowl champion Tom Brady and former NFL player Michael Strahan. A-Rod also posted a "full family" photo, which included Cordeiro and the former New York Yankees star's two daughters, Natasha and Ella.

Alex Rodriguez and Jaclyn Cordeiro's Instagram story

Jaclyn Cordeiro's boyfriend Alex Rodriguez reveals details on his HBO show

"Alex vs A-Rod" is a three-part documentary series from Religion of Sports, co-founded by Tom Brady and directed by Gotham Chopra & Erik LeDrew.

The documentary is an insight into A-Rod's career as the former Yankees star describes the show as an exploration of "a flawed man who happened to play baseball."

The most important part of the show is when A-Rod opens up about the suspension for the entire 2014 season over a scandal.

“A part of me died when I got suspended, and it cost me the Hall of Fame, which kind of really sucks. But I have no one to blame but myself,” he said. “But in many ways, it saved my life because I was able to work on the tools, rewire the brain, and make me, I believe, a better person to be, a better father, a better friend, a better owner.”

The show revolves around the evolution from his early "Alex" identity (the child prodigy) to "A-Rod" (the superstar driven at all costs) and now to "Alex" again. Seeing the turnout at the event, it seems A-Rod still has many in his corner in support after an extraordinary career, which may not earn him a spot in the Hall of Fame.