The actress and model, 52, has returned to Britain to be with 21-year-old Miles Hurley.
The incident occurred Thursday in Wandsworth, a London borough. The officials say the men are believed to have been "attacked by a group of males (no further details) who got out of a vehicle and assaulted them before fleeing the scene".
They were both taken to a hospital "where their conditions are described as not life-threatening or life-changing", police said.
London Ambulance Service took the two men to a south London hospital, where they were treated for stab wounds. Our hearts are with Elizabeth and her family during this time.
The second man, also believed to be aged 21, has been discharged but the other victim, believed to be Mr Hurley, is still being treated. "The police will be appealing for witnesses", she wrote.
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The police said that a man has been arrested in the case but it yet not clear if the attacks were related. In the first incident, a family of three were attacked.
"His family feared the worse", said a source close to the situation.
The star was pictured arriving Heathrow on Friday morning and is thought to now be at Miles' bedside with sister Kate. Fortunately, the blade missed Miles' vital organs so he's expected to recover, according The Sun.
And Liz left the US on Friday (09Mar18) to be with her family after the "appalling" incident. Miles's mother is Liz Harley's big sister and they have very close contacts, as she has given advice on the career of her nephew, who is a model.
Hurley has previously shared Mr Miles' modelling photos, tweeting: "Here's my handsome nephew".
Miles has done shoots for fashion king Roberto Carvalli and Dolce & Gabbana. The investigation is ongoing.