During the final date of his UK tour, Rod Stewart had a surprise for fans ... per the L.A. Times is the youngest of five siblings — has two living sisters, Mary and Peggy.

The 12-year-old is often seen out with his famous parents and siblings in pictures ... 37, Renee Stewart, 32, Liam, 29, and his two previous boys with Penny. Rod Stewart and Penny Lancaster ...

Rod Stewart has penned a heartfelt message to ... as were several of Liam's siblings, including sisters Sarah, Kimberly, Ruby, and Renee and brothers Sean, Alastair and Aiden.