Has been pointed to be the other woman in Sean Penn's marriage to his now-estranged wife Robin Wright Penn, Sienna Miller branded the report as "outrageously untrue" and insisted she and the actor are just friends.
The New York Daily News' columnists Rush and Molloy run a story under the headline "Sean Penn and Robin Wright Penn split up after (Sienna) Miller time", reported in it that Sienna was seen having a late night out with Sean during which she was spotted sitting on his lap with her arm around his neck while dressed sexily.
Quickly responded to the false accusation, Sienna then had her lawyer sent a "warning letter" to the New York Daily News, asked them to retract the infidelity report or else the actress will "take appropriate steps to pursue her remedies."
Called the New York Post's story "outrageous," "false," and "highly defamatory," Sienna's lawyer insisted "My client will not hesitate to file suit when necessary to protect her rights."
Rush & Molloy, elsewhere, responded "We thought we gave ample space to Sienna Miller's defenders last week when we reported on the actress' partying with Sean Penn. But now that the blogs and the Brits are putting too fine a point on the item, we'll allow Sienna's reps to say again that she did not break up Penn's marriage to Robin Wright."
Sean and Robin tied the knot on April 27, 1996. On December 27, 2007, the couple's representative announced that they were divorcing.