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Bill Cosby and Roman Polanski have been expelled from the US Academy of Motion Picture Arts and Sciences.

The academy - which runs the Oscars - said this was done in accordance with its standards of conduct.

TV star Cosby was convicted of sexual assault last month. Oscar-winning director Polanski admitted unlawful sex with a 13-year-old girl in 1977.

Producer Harvey Weinstein was kicked out last year, following numerous allegations of sexual assault.

Less than a year after the downfall of the producer the #MeToo movement is catching up with other men who abused their power, the BBC's James Cook in Los Angeles reports.

Neither Cosby nor Polanski have publicly reacted to the academy's decision.

Cosby's wife, Camille, described his conviction as "mob justice, not real justice".

"This tragedy must be undone not just for Bill Cosby, but for the country," she said.

What did the academy say?

The prestigious organisation made the announcement on Thursday - two days after its board members voted on the issue.

In a statement, it said its board "has voted to expel actor Bill Cosby and director Roman Polanski from its membership in accordance with the organisation's Standards of Conduct".

"The Board continues to encourage ethical standards that require members to uphold the Academy's values of respect for human dignity," it added.

Only four people are known to have been expelled in its 91-year history.

The first was actor Carmine Caridi, who had his membership revoked in 2004 after he allegedly sent confidential film preview videos to a friend which ended up online.

On social media, many people have been asking what took the academy so long to take action against Polanski, who has been honoured in the decades since he admitted to statutory rape.

Polanski's Oscar nominations since his 1977 guilty plea

1981 : Best Director for Tess

: Best Director for Tess 2003 : Best Picture for The Pianist

: Best Picture for The Pianist 2003: Best Director for The Pianist (which he won)

What did Polanski do?

The unlawful sex case against Polanski, now aged 84, has dragged on for more than 40 years.

Polanski admitted unlawful sex with Samantha Geimer, who was a minor in 1977, and served 42 days in prison, but later fled the US over concern that a plea bargain deal would be scrapped.

Media playback is unsupported on your device Media caption Samantha Geimer was raped by Polanski when she was 13

He has French and Polish citizenship, and has evaded various extradition attempts by US authorities.

France - where he lives - does not extradite its own citizens. A Polish court also rejected a US request when he was filming in Krakow in 2015.

The Swiss authorities also turned down a US warrant in 2010, after placing Polanski under house arrest for nine months.

Last year, he was picked to head the jury at the Césars, the French equivalent of the Oscars.

He stepped down after the move sparked outrage.

Last year, Ms Geimer told a US court she had forgiven Polanski and wanted to move on. But the court refused her plea.

Why now?

By James Cook, BBC News, Los Angeles

Why now? That's the question, isn't it?

For Bill Cosby, the answer appears obvious. A criminal conviction seems to be the standard which was applied in this case: expulsion from the academy came just one week after a guilty verdict.

Roman Polanski's expulsion, by very stark contrast, comes more than 2,000 weeks after he pleaded guilty to having sex with a minor.

Not only that but Harvey Weinstein was expelled without a criminal conviction although he faces (and denies) allegations of rape.

So why did it take Hollywood more than 40 years to decide that the statutory rape of a 13-year-old was beneath its precious "values of respect for human dignity"?

The academy recently implemented revised standards of conduct for its 8,400 members, including a provision to suspend or expel those who "compromise the integrity" of the organisation.

The real answer though does not lie in bureaucracy but in shame. The industry has been shamed into action by the disinfecting sunlight of the #MeToo and Time's Up movements.

The problem for the academy is that this harsh glare is shining on many other members and with each expulsion the pressure grows to act in those cases too.

What about Cosby's conviction?

In April, Cosby, 80, was found guilty of three counts of sexual assault, each of which carries a potential 10 years in prison.

He was on trial for drugging and assaulting ex-basketball player Andrea Constand in 2004.

It was the second time the actor had stood trial for the allegations, after an earlier jury failed to reach a verdict in 2017.

Cosby starred in sitcom The Cosby Show, which was a global hit and ran from 1984-92. Cosby was widely known as "America's Dad" for his fatherly role in the comedy.

At one point, he was the highest-paid actor in the US.