It is not the first time Stewart has had a stand-off with Ultimo's boss, Michelle Mone.

Rachel Hunter, left, Rod's ex-wife and Kimberly Stewart, third
in line to the underwear throne

When the firm dumped his wife Penny Lancaster in favour of his ex-wife Rachel Hunter in 2004, he called Mrs Mone a "manipulative cow".

A source said: "Apparently he decided he was going to make Ruby concentrate on her musical career, but Michelle is in no doubt it's because of her involvement with Ultimo."

Mrs Mone confirmed that Ruby had been signed but said she was doing her last shoot.