Kristen Stewart is reportedly planning to write an apology letter to Rupert Sanders' wife.

The 22-year-old actress - who made a public apology to her boyfriend Robert Pattinson yesterday (25.07.12) for cheating on him with the director - is seeking forgiveness from British model Liberty Ross and decided to do so in private as she "didn't feel it was appropriate" to include her in her statement.

A source said: "Kristen didn't feel it was appropriate to issue a public apology to Liberty once the story of her affair with Rupert broke.

"Instead, she's going to do the decent thing and write Liberty a private letter expressing her deepest regret for her actions.

"She was thinking of including Liberty, Rupert and the kids in her public apology - but Kristen was so desperate to save her relationship with Rob she decided to concentrate on that first."

Kristen feels "awful" about her illicit affair, particularly because Rupert and Liberty have two young children, Skyla and Tennyson.

The source added to a media website: "Kristen feels she made a terribly naive mistake and will do anything to make amends. The fact that Liberty and Rupert have two kids has now dawned on her and she feels awful for what she did."

Kristen described the relationship as a "momentary indiscretion" in her apology yesterday.

She said: "I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. This momentary indiscretion has jeopardised the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry."

Rupert also issued an apology, saying he was "utterly distraught" about his actions.

He said: "I am utterly distraught about the pain I have caused my family.

"My beautiful wife and heavenly children are all I have in this world. I love them with all my heart. I am praying that we can get through this together."