Common: Serena Got Married? Didn't Know, But Congrats!

Here's Common saying he had NO IDEA his ex-girlfriend, Serena Williams, tied the knot last week ... but he's congratulating her anyway in one of the most interesting clips of the day.

Common and Serena were one of Hollywood's "It" couples earlier this decade -- so when we got him out at Equinox gym in L.A. we asked him what he thought of his old flame tying the knot.

"Nah, I didn't see it ... but God bless her. That's the queen! She's the queen! Congratulations to them!"

Serena's wedding was a massive celebrity-filled mega-event -- with stars like Beyonce, Kim Kardashian and Ciara in attendance.

One last thing ... Common follows both Serena and Vogue on Instagram (Vogue posted a ton of Serena's wedding pics) -- so, we gotta ask ...