The 38-year-old actress and the baseball player are said to have called time on their relationship after over 18 months of dating in order to concentrate on their careers.
A source told Us Weekly magazine: "They broke up recently. She`s very busy with her career and he`s had injuries and wants to focus on his game. They`re dedicated professionals."
Despite their break-up, the pair intend to remain friends.
The source added: "They`re still very friendly and like each other. They have an enormous amount of respect for each other."
Cameron - who was first rumoured to havesplit from Alex in June - recently revealed she realised how much she loved Alex when she let him eat the last of her popcorn at the Superbowl in Miami in February, something she would usually not be happy with.
She said: "We were watching the game, and I was eating, and I was getting down to, like, the last couple pieces of popcorn.
"And all of a sudden, I see [Alex`s] hand coming in. Anybody who knows me does not put their hand in my food, especially when it`s close to my mouth.
"I said, `What are you doing?` And then I went, `You know what? I love you too much, I`m going to give it to you. You deserve it.` "