Prince Andrew's ex wife looked tense as the Scotsman inched towards the finish line. Meanwhile, Beatrice and Eugenie threw their arms in the air with joy.
Eugenie is a keen cyclist herself. The 22-year-old recently took part in London's Nightrider event – a 64 mile charity night time bike ride past 50 of the capital's most famous landmarks.
Her sister is well known for her interest in running, having taken part in the capital's marathon before.
The mother-daughters team weren't the only VIP spectators watching Sir Chris pick up his sixth gold medal.
Prince Harry was a bundle of nerves during the evening's events. The flame-haired royal was up out of his seat urging Laura Trott to first place in the 500-metre time trial.
His cheers weren't enough to help Victoria Pendleton ride to victory, however. The 31-year-old came in second in her sprint final, pipped to the post by her arch rival Australia's Anna Mears.
Harry put his head in his hands as the Aussie cyclist triumphed.
Other famous faces watching the action included former Prime Minister John Major and Lord Seb Coe.