Sean Penn and Charlize Theron

The 53-year-old actor and the 38-year-old beauty were seen leaving her Hollywood property in separate cars shortly after returning from Hawaii, where they holidayed at Sean's abode.

The pair were spotted soaking up the sun in their bathing suits over the new year as they spent time relaxing on a beach in Hawaii near the 'Gangster Squad' star's home.

Speaking to the New York Daily News, an eye-witness described them as looking "very close and comfortable together".

Sean - who was previously married to Madonna and has dated several stars including Scarlett Johansson – and Charlize have known each other for years but their latest jaunt has fueled recent speculation they could be dating.

Charlize has two-year-old son Jackson – who she adopted in 2012 - but there was no sign of him as she holidayed with Sean to see in the new year.

The dazzling blonde is said to be keen to adopt another little one this year so Jackson can have a sibling to play with.

A source recently said: "Charlize admits it's a lot to go through, but she definitely wants Jackson to have a little brother. She's starting the process all over again right after the new year. She wants Jackson to have a sibling who isn't four or five years younger than him - she wants to raise them together."