Charlize Theron has fuelled rumours she and Sean Penn are set to wed

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.

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

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.

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

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.

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

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.

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."