Wandering Jude Law (search) can kiss his fiancée goodbye.

A "nuclear" Sienna Miller (search) ripped off her engagement ring and warned pals that her planned wedding to the 32-year-old "Alfie" star is likely kaput — despite two days of desperate face-to-face meetings in which the red-eyed hunk begged the actress to forgive him for cheating on her with his kids' nanny, it was reported Tuesday.

"Sienna is probably too angry for tears at the moment," said her equally incensed mom, Jo. "It is anger and betrayal.

"Never in a million years would I have suspected that he would do that to my daughter.

"We have been speaking regularly, and neither of us has had too much sleep," she said of 23-year-old Miller. "But she is an absolute trouper, my Sienna.

"Sienna is not with Jude at the moment," the mom said. "She has spent the last couple of days in the country, staying with friends. I can't comment on whether they will stay together."

In a defiant fit of anger toward her shame-faced fiancé, Miller refused to wear her diamond-encrusted engagement ring Monday night when she headed into the London's Wyndham Theatre to star in "As You Like It."

Despite the emotional turmoil, Miller managed to deliver a performance worthy of a rousing ovation. She fled the stage in tears afterward.

Miller was apparently still devastated Tuesday: A notice was posted on the theater door canceling her appearance Tuesday night.

One pal told the London Sun that Miller reacted "like a nuclear explosion" after reading nubile nanny Daisy Wright's (search) diary excerpts in Sunday's Mirror detailing her and Law's steamy sexcapades.

And Miller may only get more incensed. The Sun yesterday reported that at least once, Law begged Wright, 26, to join him in a kinky threesome with an unidentified woman in the United States.

Wright balked, saying "she just isn't that kind of girl."

The revelation came a day after Law took the stunning step of admitting he cheated on Miller.

The Mirror said Miller spent Monday poring over Law's statement. "It made her feel [only] marginally better to discover he was so contrite," a pal said.

Law is reportedly devastated about hurting Miller, but Wright said he whined while seducing her that Miller was never home for him.