Liam was out shopping in L.A. ... when a photog congratulated him on his reported reengagement. Until now, it's been mostly Miley's friends doing all the talking -- so, this was the perfect chance for him to finally say his peace.
As we told you, Miley and her pets moved into Liam's Malibu home recently.
Check out Liam's reaction to all the big changes in his life. Let's just say ... he's more the strong, silent type.