Conor McGregor Arrives at Church for Sister's Wedding

Conor McGregor got all cleaned up this weekend for for his sister wedding.

"The Notorious" was all smiles as he assumed the role of groomsman on Aoife's big day. She tied the knot at St. Mary's Church in Enniskerry, Ireland on New Year's Eve.

Conor's pregnant baby mama was a bridesmaid.

Knowing how Conor likes to celebrate ... it musta been one hella reception.