The former Spice Girl was one of the celebrities offered the prestigious opportunity to record a few words offering The Queen their congratulations on her 70-year reign during Saturday's Platinum Party at the Palace, which aired on BBC One.
But it seems some viewers felt that Horner got the tone a little wrong in a tribute that was branded "super weird".
Horner, 49, appeared as part of a famous face video tribute where she shared her feelings on the Jubilee.
She said: "Our Queen, kind... loving... strong... serving our country, the Commonwealth, uniting us all together.
"Always putting others before yourself, you're truly inspirational, inside and out, we thank you... we love you."
Read more: Charles pays moving Jubilee tribute to Queen
The reaction to her message was a little confused as viewers questioned the intensity of her words.
One person tweeted: "Um, that was super weird from Geri Halliwell..."
Someone else added: "Blimey, Geri Halliwell being completely over the top there."
Another viewer commented: "Lord, Geri Horner, that was a bit intense."
Someone else joked: "I’m sure the Queen has always wanted a recorded message from Michael Buble and Geri Halliwell."
Platinum Party at the Palace included performances from Queen and Adam Lambert, Diversity, Sam Ryder, Diana Ross, Elton John, Rod Stewart and Lin-Manuel Miranda.
While The Queen was not in attendance at the Buckingham Palace event, she still managed to delight viewers with an unexpected appearance in a humorous sketch with Paddington Bear, where they sat down to afternoon tea together.
The scene showed Paddington telling The Queen that he always kept his favourite snack, a marmalade sandwich, to hand as she replied: "So do I."
She then produced a marmalade sandwich from her handbag, saying: "I keep mine in here. For later."
Watch: Prince of Wales' tribute to The Queen at Jubilee party