The 40-year-old, who has been laying low after sexual harassment allegations surfaced earlier this year, looked carefree when he was seen taking a dip.
The couple was also seen holidaying in Santorini recently.
Franco was nominated for an Academy Award for Best Actor for his role in the 2010 film 127 Hours.
He is known for his roles in live-action films such The Disaster Artist (2017), for which he won a Golden Globe Award for Best Actor.
Aside from film, he is also known for his work on television; his first prominent acting role was the character Daniel Desario on the short-lived ensemble comedy-drama Freaks and Geeks (1999–2000), which developed a cult following.
He portrayed the title character in the television biographical film James Dean (2001), for which he won a Golden Globe Award.