Post Malone Apologizes to Fans with Free Shirts During Boston Makeup Show

Post Malone went out of his way to make things up to his fans in Boston ... giving out free shirts and a huge apology to folks at his show.

Post hit the stage Monday night, performing for fans in Bean Town after his recent rib injury forced him to cancel his concert there a few weeks ago.

He told the crowd, "I'm so f***ing sorry and I just wanted to say thank you for coming out tonight ladies and gentlemen. It means the f***ing world to me".

Besides putting on a great show, Post also let fans know they could grab a T-shirt on their way out. Talk about a sweet bonus -- that's legit official custom Boston merch, not some parking lot copycat gear!

As we reported ... PM pulled the plug on his Boston concert last month, just a few hours before showtime.

You'll recall, the singer had taken a huge fall onstage, a few nights prior during a show in St. Louis ... and he ended up fracturing a rib.

At the time, he said he was in too much pain to perform and was struggling with his breathing. He returned to the stage a week later in Cleveland.