The 'Cruel Intentions' stars ended their marriage in 2008 and are parents to Deacon and Ava.
Phillippe took to Instagram to post about the occasion and share some pictures featuring his and Witherspoon's lookalike kids, Deacon and 23-year-old Ava.
"Awesome night w family & friends celebrating the release of A New Earth by @deaconphillippe!! Thank you so much to everyone who attended and to our sponsors: @drinkmamitas @tequilaavion & @soliscatequila Also, special thanks to @staffordschlitt @melroseplacela and my dawg @benmassing for helping me w the setup in very few balloons. Stream, download, and listen to the album.😊#AOTY Photos by: @simplyyvan who crushed it," the 48-year-old actor wrote.
The pics included one of Phillippe and his son linking arms as they smiled for the camera. The next photo included Deacon smiling as he stood in between Witherspoon and Ava. The photo set also included a picture of Phillippe having a proud dad moment as he spoke on the microphone.
Deacon too posted pics to his Instagram from the event, and featured his family. "Careful where you step we on a mission♠️❤️whatta night," he wrote.
Witherspoon and Phillippe were married from 1999 to 2008. Witherspoon went on to wed Jim Toth in 2011, though the pair, who are parents of 10-year-old son Tennessee, recently announced they were ending their marriage.
As for Phillippe, he is also dad to 11-year-old daughter Kai Knapp.
This isn't the first time Witherspoon has reunited with her ex-husband. Last year, the two put on smiling faces as they celebrated Deacon's homeschool-high school graduation. They also met up for Deacon's 18th birthday bash.
In February, Phillippe had a proud dad moment as he dished about Deacon's future in music, and shared if either of his kids are following in their parents footsteps.
"The focus is really music, that's what he's in school for right now," he shared. "He may dabble in acting at some point but he's got a great album about to come out, and he's looking at signing with a label soon. So, that's going to be his focus."
As for Ava, Phillippe said she's "undecided" about acting, but teased, "You never know what'll happen in the future."