Lukas Gage is reacting to his ex-husband Chris Appleton announcing an upcoming self-help memoir on the heels of Lukas' upcoming book ... and it sounds like he's throwing some shade.

We got the actor outside DOGPOUND Gym in West Hollywood on Monday and our photog asked him about Chris recently announcing a self-help memoir. Hanover Square Press

Lukas says he didn't know about it but feels "honored" to be so "influential" with the timing of his ex's book.

LG's book, "I Wrote This For Attention," is due out in October and Chris' "Your Roots Don't Define You," drops in January ... just 3 months after Lukas'. Play video content

We asked Lukas some follow-up questions, but it seemed like he didn't want to take any more perceived shots at Chris ... though he may have sarcastically s

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