The Apprentice star said the coronavirus had "got her" two weeks after Derek was also killed by the coronavirus.
Lord Sugar, 73, shared a photo of his sister to Twitter on Wednesday morning, writing: "My eldest sister Shirley passed away today at the age of 88 she had been sick for a while but I guess covid got her in the end to join our brother Derek who passed 2 weeks ago . RIP SHIRL."
My eldest sister Shirley passed away today at the age of 88 she had been sick for a while but I guess covid got her in the end to join our brother Derek who passed 2 weeks ago . RIP SHIRL pic.twitter.com/IldwzQS6WP
— Lord Sugar (@Lord_Sugar) December 30, 2020
On 15 December, he said his brother had died after COVID had complicated his underlying health issues.
Lord Sugar said: "My brother Derek died today another victim of Covid which complicated his underlying health problems.
"He was a life long Spurs fan and my sister in law made me laugh in 1991 thanking me for buying Spurs for him.
"He will be sadly missed by the whole family. RIP BRO.”
Watch: 2020 - the year of the pandemic
This year's series of The Apprentice has been postponed due to the coronavirus.
The show typically airs in October after being prerecorded earlier in the year. Scenes of the star picking his new business partner air in December.
The contestants also usually live together for the duration of the competition.
A BBC spokesman confirmed back in June: “Sadly we have decided to postpone The Apprentice for 2020.
"Production safety and the wellbeing of everyone involved in the show is our number one priority.”
Watch: The stars we’ve lost in 2020