Michael Phelps was among a star-studded group of flag-bearers at opening ceremonies of the Special Olympics World Games in Los Angeles Saturday.

Unlike traditional opening ceremonies at international sporting events, athletes filed into the Special Olympics World Games without holding national flags. Instead, a group of Special Olympic and Olympic athletes carried in the Special Olympics flag together.

Phelps was one of those athletes, joining diver Greg Louganis and figure skater Michelle Kwan, according to ABC News.

Phelps, the most decorated Olympian of all-time, has been partnering with the Special Olympics since at least 2007. Most recently, he ran a Special Olympics swim clinic for 5 Baltimore-based athletes who were preparing for these World Games.

The World Games bring together 6,500 athletes from 165 countries, according to ABC. That makes it the largest athletic event to take place in Los Angeles since the 1972 Olympic Games.

The Opening Ceremonies were a “who’s-who” of celebrity appearances. Avril Lavigne and Stevie Wonder were among the musical performers, and late-night talk show host Jimmy Kimmel spoke to open the ceremonies.

Even the President and First Lady got involved. Michelle Obama spoke to the athletes during the ceremony, and her husband, President Barack Obama, made a video appearance to welcome the athletes to the Games.