Moore took to Instagram to share the sweet moment when the pair bumped into each other on Saturday at the Veuve Clicquot Polo Classic.
The 34-year-old also hung out with Olivia Wilde and her This Is Us co-star Justin Hartley plus his wife Chrishell.
The actress was all smiles as she and Valderrama cosied up to his ex, making a pout as they smiled for a selfie.
Moore, 34, and Valderrama, 38, were an item back in 2000, before ending things two years later in 2002.
Back in June, Moore confessed that her romance with The 70s Show actor was a turning point in her life.
Explaining that they met when she was 15 and that she had “never French-kissed a boy”, Moore said, “He was like my first, real, true boyfriend.”
While the former couple don't hang out regularly - Moore has nothing but praise for her former flame.
“We’re not that close, but we’re friendly,” she explained. “He’s a good guy, he really is.”
Despite their friendship, Moore denies the actor's claim that he was the man that took her virginity.
Back in 2006 Elle reported that Valderrama told Stern, “The sex with Mandy was good, but it wasn’t like warm apple pie.”
Moore responded at the time saying he ex's comments were “utterly tacky, not even true” and that “it hurt my feelings because I like him.”
In her most recent Stern chat, Moore clarified that “he did not” take her virginity.
“I dated him when I was 16 and 17. No. I love him and I still love him and he’s a very good friend, and that’s why I was so shocked by it. Because not only was it a fib, but it was so unlike him — it was so uncharacteristic.”