Zsa Zsa Gabor's adopted son Oliver Prinz von Anhalt died the same day as her

Oliver Prinz von Anhalt pictured in 2007. Photo / Splash News

Zsa Zsa Gabor's adopted son Oliver Prinz von Anhalt has died.

The 45-year-old son of Frederic Prinz von Anhalt was critically injured in a motorcycle crash in Los Angeles on December 18, the same day that Gabor died at home at the age of 99, the Daily Mail reports.

Zsa Zsa Gabor pictured in 1986. Photo / AP

Oliver was hospitalised, but died from his injuries on Sunday, according to his brother Marcus Prinz Von Anhalt.

The German businessman was in a coma after the crash but never woke.

Marcus took to social media to express his sadness, telling friends and fans his brother was killed when his motorcycle collided with a truck.

Oliver, who was known as Oliver Bendig before being adopted as an adult, had flown to Los Angeles just the day before, after visiting his brother in Germany.

Marcus shared a tribute video on Instagram on Monday and said: 'Forever Brothers!!! Live the Afterlife in the fullest like you did before!'

The pair were not blood brothers but were adopted later in life by Zsa Zsa and Frederic. Frederic, the self-styled "Prince Frederic of Anhalt, Duke of Saxony and Westphalia, Count of Ascania" has boasted about adopting people who paid him to have his royal title, even though the validity of the title is widely disputed.

Grief-stricken, Marcus also posted on Facebook: 'My brother! You will stay forever in my heart. I can't understand the world! Why?'

It was alleged that his father Frederic didn't know about the crash until he heard from a coroner on Monday evening. Frederic told TMZ he believed his son was in Germany at the time.

According to German site Bild - the first to report Oliver's death - Frederic had disinherited his adopted son in 2010. It is not clear why.