Selena Gomez's Mom Thrilled Her Grandfather Walked Her Down the Aisle

Selena Gomez's grandfather proudly gave her away during her fairytale wedding to Benny Blanco on Saturday ... and we're told the decision was a no-brainer.

A family source tells TMZ ... Selena chose her maternal grandfather, David, to walk her down the aisle because she's extremely close to him, and he never got a chance to walk his own daughter, Mandy, down the aisle because she eloped.

Our sources add ... her stepfather Brian has his and Mandy's daughter Gracie to eventually walk down the aisle. We're told by an additional source Selena is quite close to Brian.

Furthermore, our family source says Selena's mom thought having her grandfather give her away was a "thoughtful gesture."

Mandy, who co-founded Wondermind with Selena -- even raved about the wedding on Instagram Sunday, writing ... "The evening couldn’t have been more beautiful and perfect! Absolutely flawless!"

She went on ... "It was a fairytale come true and it was beyond heartwarming watching my father walk her down the aisle!!!"

It's no secret Selena is super tight with her maternal grandparents -- she lived with them for years and they've made appearances on her cooking show, "Selena + Chef."

The "Only Murders in the Building" actress' dad, Rick, was present as she said "I do" to Benny ... and sources say their relationship is pretty solid as well. However, it's unclear how he ultimately felt about her decision to have her grandfather give her away.