The Mysterious Girl singer was dapper for the engagement at No 10, pictured in a crisp white shirt and slim burgundy tie. He had a bottle of water in his hands as he beamed for the camera.
Later on, the 41-year-old shared another snap – this time of himself and his pretty brunette partner Emily. The photo of the couple was taken outside the iconic entrance with "No 10" in clear view.
A royal blue blazer completed the star's look, while Emily appears to be in a monochrome number with a statement necklace and her brunette locks worn loose. Peter wrote alongside the picture: "It's not everyday.... Fantastic eve. Can't wait to tell you about it Thurs."
The popular TV personality has been involved with Cancer Research UK since he set up the Peter Andre Fund after losing his brother Andrew, who sadly died of cancer in late 2012.
Speaking about the loss of his brother, who died two years ago on 17 December, Peter said that his fiancée Emily helped him tremendously. "Everything changed when I lost my brother," he told the Daily Mirror.
"All my worst fears came out and I was a mess for so long.
"If you say 'commitment issues' it sounds like it's from previous relationships," he added. "But my phobia came from losing him because I didn't want to lose someone again. That threw me into turmoil.
He continued: "But the genius Emily has made me so much better. What helped is that while I'm an emotional thinker she is a logical thinker. Honestly I don't think I could have got through it without Emily. I would have gone into my own shell."