The Duchess, who has continued to live in the same grounds of the Royal Lodge, the Queen Mother's former country home, with the Duke since their divorce 17 years ago, denied reports that they were a couple again.
A spokesman for Sarah said: "They continue to be joint parents and best friends and try to set the best example for the girls."
The pair, who divorced in 1996, have remained good friends since their split, often taking holidays together with their two daughters Princesses Beatrice, 25, and Eugenie, 23.
They have maintained a united front as parents, raising their daughters together and both attending and posing for photographs at significant family occasions, such as Beatrice’s graduation ceremony at Goldsmiths College in London in 2011.
Reports of the romantic reunion were fuelled by Sarah’s visit to Balmoral earlier this month. She joined her ex-husband and their daughters for a weekend at the Scottish retreat with the Queen.
It is believed to be the first time the reigning monarch had invited her former daughter-in-law back to the castle since 1992, after an incident involving Sarah caused embarrassment for the royal family.
"We got divorced because I had to go out to work, and Andrew and I believed that it wasn't right for me to be commercial while I was still in the royal family," Sarah has said of their divorce in the past.
Prince Andrew, 53, has continued to provide financial support for his ex-wife, also aged 53.