Charlize Theron has fueled rumors she and Sean Penn are set to wed.

The 38-year-old actress - who has been romancing the Milk star for eight months - was spotted in Los Angeles International airport on Wednesday sporting a huge diamond ring on her engagement finger, prompting speculation her 53-year-old beau has proposed.

The sighting of the ring comes just a week after it was claimed the pair are planning to tie the knot in the Snow White and the Huntsman star's native South Africa in the coming months. "They want to get married very soon," a source said.

And Charlize - who has two-year-old adopted son Jackson - is reportedly keen to adopt a child with Sean shortly after they've exchanged vows. "Charlize always intended to have another child," the insider added.

Sean - who already has 23-year-old daughter Dylan and 20-year-old son Hopper with his ex-wife Robin Wright - has also been bonding with Charlize's young son. "He is a father figure to him," the insider said.

Meanwhile, the loved-up pair - who have known each other for 18 years - have watched each other change over the years and are looking forward to a positive future together as a couple. "Charlize has seen Sean grow up. He's a wiser soul and much more patient. They're looking to the future with a lot of hope," the source explained.