Theron spotted with ring on engagement finger

Charlize Theron has fuelled rumours 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 partner has proposed.

The sighting 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.

A source said: "They want to get married very soon."

Theron - who has two-year-old adopted son Jackson - is reportedly keen to adopt a child with Penn shortly after they have exchanged vows.

The insider added: "Charlize always intended to have another child."

Penn - 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 Theron's young son.

The insider added: "He is a father figure to him."

Meanwhile, the 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.

The source explained: "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."