'Billions' Season 4 Premiere Dedicated to Dennis Shields

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'Billions' co-creator Brian Koppelman

The New York banker and ex of 'Real Housewives' star Bethenny Frankel, who died in August, was close with the Showtime series' co-creator Brian Koppelman.

Billions returned to Showtime for its fourth season on Sunday night and ended with the following note: "In memory of Dennis Shields."

Shields, who died in August of an apparent prescription drug overdose at age 51, was more recently known for dating Real Housewives of New York City star Bethenny Frankel. But it turns out that the late banker was good friends with Billions co-creator Brian Koppelman, who on Sunday night called Shields his "brother" in a tweet: "Dedicated to Dennis Shields, our brother."

At the time of Shields' death, Koppelman took to Twitter to express his grief and share more insight about their friendship.

"Dennis Shields, who died this morning, was my close friend for 30 years. One of the smartest, most generous, people I ever came across," the Ocean’s Thirteen scribe tweeted. "He was also one of the great storytellers in the world. And understood life’s endless absurdity in his bones. I loved him. And his family."

According to Koppelman, Shields had a major influence on his work in Hollywood. The writer-producer had also reflected on Shields' small part in his 2009 film The Girlfriend Experience, a project Koppelman helmed alongside Billions co-creator David Levien.

"Dennis had a huge impact on my life. But also on my work w Dave through the years. Each of our movies contains a piece of him," Koppelman added in a follow-up tweet not long after Shields' passing. "There would be no Grama without him. No 500 fights. And definitely no guy in a diaper in The Girlfriend Experience (that was actually Dennis in a cameo)."

On Monday morning, Shields' ex Frankel responded to a tweet from a fan who asked how the financier was connected the hit Showtime drama. "We are all connected and have a long history," wrote the Bravo personality, who introduced Shields to her longtime friend Koppelman years ago. "He is really missed and touched so many people’s lives."

Billions airs on Showtime Sundays at 9 p.m.