The 28-year-old model - who tied the knot with aerospace worker James Cook in May - is constantly amazed by her friend's ability to pull off any trend and claims even her own engagement ring looks better on Alexa.
The star told Net-a-Porter's The Edit: ''Everything she wears she makes desirable. I told her to try my engagement ring on once and I fell in love with it even more seeing it on her finger.''
Poppy claims she has coveted Alexa's effortless style from the very first time they met in the Storm Models waiting room 10 years ago.
She recalled: ''I remember thinking she was very beautiful, almost cat-like, but definitely a bit of a bloke. She was wearing skinny jeans that I wanted/needed in my life immediately - a feeling I had no idea would resonate every time I saw her.''
And the blonde, who is the older sister of Cara Delevingne, says her jealousy spirals out of control when she goes on holiday with Alexa.
Poppy joked: ''She will bring a suitcase the size of a piece of calamari and yet each day she'll wear something mouth-wateringly stylish.''