The pair were watching the spectacle from the royal box when Mike was pictured giving Louis the, 'I've got my eye on you' sign while pointing his middle and forefingers towards his eyes.
WATCH: Kate Middleton tries to stop Louis sucking his thumb
The Duchess of Cambridge, who was sitting next to the four-year-old, could be seen laughing at the humorous exchange between her son and the former rugby player.
The three royals were joined by the Duke of Cambridge, Zara Tindall, Prince George and Princess Charlotte, as well as Prince Charles and the Duchess of Cornwall among other senior members of the family for the pageant.
The incredible event is split into four acts: For Queen and Country with a military parade; The Time of Our Lives which will delve into seven decades of culture, music and fashion; Let's Celebrate, which tells the story of the Queen's life in 12 chapters with corgi puppets and carnival creations; and the Happy and Glorious musical spectacle which will see performances from stars of the music, comedy, film and arts world.
The royals watched the spectacle on Sunday
Ed Sheeran is set to bring the four-day celebration to a close with a performance that will pay a special tribute to the Queen's remarkable 70 years on the throne.
The sweet moment between Prince Louis and Mike comes just days after the youngest child of the Duke and Duchess of Cambridge was pictured pulling faces at the crowds from the Buckingham Palace balcony while watching the military flypast at Trooping the Colour on Thursday.
Prince Louis pulled faces while on the Buckingham Palace balcony on Thursday
The young prince was seen happily waving towards the sky before later holding his hands over his ears as the aircraft flew overhead, at which point Kate was spotted bending down to have a word with him.
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