Joined by brothers Brooklyn and Cruz, the 12 year old completed the children’s race in the British capital.
All the family wore specially made Team Romeo t-shirts to support Romeo as he completed the three mile course.
Victoria posted a picture on Twitter to reveal how proud she was of her second son.
She wrote: “Well done Romeo! We are all so proud! Running London Marathon for UNAIDS and 7 Fun.”
She also added a picture of banners the family had made.
Brooklyn also posted a supportive picture on his Instagram.
A large number of celebrities are taking part in the main event today.
©OK Magazine