Buffalo Bills Superfan 'Pancho Billa' Dead After Cancer Battle

1:12 PM PT -- TMZ Sports talked to Bills legend Andre Reed -- who spent time with Pancho at the 2018 NFL Draft ... and the HOF'er reflected on his tragic passing.

Beloved Buffalo Bills fan Ezra Castro -- better known as "Pancho Billa" -- has died after a long battle with cancer ... his family announced Tuesday.

"Our hearts broken as we have lost our dear brother ezra "Pancho Billa" this morning," the family said in a statement.

"We are thankful and forever grateful for all the love and support during this journey. Ezra was surrounded by family and loved ones."

If you've ever seen a Bills game since 2008, you've probably noticed Pancho -- whose trademark sombrero and mask costume was a huge hit among Bills Mafia. He was the first fan inducted into the Buffalo Fan Wall of Fame late last year.

When he was diagnosed with stage 4 cancer after a mass was discovered on his spine in 2017, the team rallied around Pancho and hosted him at games and the team facilities.

The 39-year-old Pancho played a big role in the Bills drafts the past 2 seasons ... personally announcing their 3rd round pick on stage in 2018 ... and gave GM Brandon Beane his stamp of approval before the team picked Ed Oliver with their first round pick last month.

Oliver visited Pancho in the hospital last week ... and even Bills legend Jim Kelly has shown support during his battle.

A GoFundMe has been set up for Pancho ... with all donations going to his family.