Scarlett Johansson brings Sean Penn to Reese's wedding

Scarlett Johansson brought Sean Penn to Reese Witherspoon's wedding to Jim Toth on Saturday.

Merritt, Loccisano/Getty

Scarlett Johansson brought Sean Penn to Reese Witherspoon's wedding to Jim Toth on Saturday.

Reese Witherspoon and Jim Toth weren't the only ones to make it official Saturday.

Scarlett Johansson and Sean Penn's joint appearance at the couple's nuptials erased any lingering doubt as to whether the two actors might just be really good friends.

The lovebirds were among the long list of A-list celebrities who turned out for Witherspoon's wedding at her Ojai, Calif., estate ? but not both of them were invited, according to PopEater.com.

"Scarlett is Jim's client, but no one, including the bride, knew she would have turned up with Sean Penn," a source close to Johansson told the site.

"Turning up at a wedding with your boyfriend is definitely a huge statement, especially that wedding," the source continued. "What it's doing is announcing to the whole of Hollywood that they are serious."

PICTURES: BLUSHING CELEBRITY BRIDES

Though photos of Johansson, 26, and Penn, 50, at the wedding have yet to emerge, the pair hasn't exactly been camera shy.

They've been photographed enjoying each other's company in Cabo San Lucas, Mexico, and L.A., with Johansson even resting her leg in the actor's lap in one of the pics.

"Scarlett is head over heals in love with Sean," a source claimed to PopEater. "She normally tries to hide away from public attention, but when she's with Sean she doesn't care."

Among the other reported guests at Witherspoon and Toth's wedding were fellow couples Matthew McConaughey and longtime girlfriend Camila Alves, Isla Fisher and husband Sacha Baron Cohen, and Alyssa Milano and husband David Bugliari, who works with Toth at CAA.

Marisa Tomei Michelle Behennah LeAnn Rimes Lindsay Price Rebecca Romijn