The Oscar victor, 59, is rumoured to have tied the knot with his 28-year-old girlfriend this week, according to a congratulatory Instagram post shared by Penn's friend and philanthropist Irena Medavoy.
Irena is a philanthropist who is married to legendary movie producer Mike Medavoy.
"Thank you for being like family a son to mike we are over the moon to (see you) find your soul mate true partner... true love that also changes the world for better... God Bless you both and the family you have joined", she wrote. "Introducing the Penn's #marriage".
A close up of Leila George's alleged engagement ring shared by Irena Medavoy.
Sean and Leila started dating back in 2016. George helped organise an fundraiser earlier this year in support of wildlife relief after Australia's devastating bushfires. "I wouldn't be here smiling today if it wasn't for him".
Despite being in the public eye, the pair have been notoriously private about their relationship.
In 2014, the Mystic River actor was believed to have been engaged to his then-girlfriend Charlize Theron, however the Bombshell star just last month said that was never actually the case. Her gold band matched Sean's.
"We are so happy for @leilageorge #seanpenn getting married". "No, we dated, that was literally all we did, we dated".
Penn was previously married to Madonna and Robin Wright- with whom he has two children- 29-year-old Dylan and 26-year-old Hopper Jack.