The Boston Celtics star Kyrie Irving has officially become a member of the Standing Rock Sioux.

Irving and his older sister, Asia Irving, took part on Thursday in a traditional Native American ceremony recognizing their tribal heritage and support for the tribe’s long battle against the Dakota Access oil pipeline. They were honored with Lakota names during a ritual in a packed auditorium that tribal spokeswoman Danielle Finn said “is a very special rite of passage for a Lakota person.” Kyrie and Asia were given the names Little Mountain and Buffalo Woman respectively.

The Irvings’ late mother, Elizabeth Ann Larson, was a member of the tribe and lived on the reservation until her adoption at a young age. She died when Irving was four. Tribal chairman Mike Faith said: “We’re welcoming home two of our own.”

The naming ceremony is complete.

Kyrie Irving was given the name “Little Mountain.” His sister, Asia, was given the name, “Buffalo Woman.” https://t.co/JNgwPpi3O1 pic.twitter.com/eWnwC8hGWj — Tim Bontemps (@TimBontemps) August 23, 2018

Irving first mentioned that his mother was a member of the tribe in 2016, and elders discovered that his grandparents were from the White Mountain family in Standing Rock. Irving has a tattoo of the tribe’s symbol and has donated to the tribe. Many of the Standing Rock Sioux have been given up for adoption and the tribe is hoping Irving’s case will help others track down their heritage.

Kyrie Irving, who won an NBA championship with the Cleveland Cavaliers in 2016, was born in Australia and grew up in New Jersey.