Alastair Stewart, 18, is the son of Penny Lancaster and Rod Stewart.
The pair also share Aiden Stewart, with Rod having six more children from previous relationships.
Many of the Stewarts have taken to Instagram to praise Alastair as his face appears in the Milan fashion campaign.
The seventh Stewart child signed a deal with luxury clothing brand Palm Angels, resulting in his face being plastered over signs and billboards across Milan.
Rod took to Instagram, sharing the billboard with the comment: “Love @palmangels and that my boy ‘wears it well’ #fashion #streetwear #milano.” (sic)
Likewise, Penny wrote: “Congratulations @palmangels for the opening of their new store in Milano and it’s my boy up there, so proud.”