Friendly exes Fergie and Josh Duhamel reunited Saturday at their son's birthday party. The 43-year-old singer and 45-year-old actor threw Axl Jack a superhero-themed fete ahead of his fifth birthday. Axl officially turns five on Wednesday. Fergie shared a photo on Instagram of herself and Axl at the celebration. "The Four" host dressed up as Wonder Woman, while Axl wore a Spider-Man costume. "happy bday party day to my favorite superhero #axljack," Fergie captioned the post. Duhamel thanked Coolhaus ice cream for providing the desserts. The premium ice cream company was founded by Natasha Case and Freya Estreller in 2009. "Thanks for showing up for my boy's birthday party @coolhaus kids went crazy. (Love you AM) #ibuywomenowned," Duhamel wrote. Fergie and Duhamel announced their split in September after more than eight years of marriage. Duhamel told E! News in January he has maintained a "great relationship" with Fergie since their divorce. "It's going really well," the actor said. "She's a great mother." "All we want is the best for our son, so it's a bit of a juggling act but we're both grownups who can handle a lot," he added. "And he's happy. That's the main thing."