Thomas Markle tells TMZ … he sent Meghan flowers for her 40th birthday, along with a personalized card that simply said, "Wishing you a happy birthday and brighter days."

We're told the bouquet featured a dozen red roses with 2 yellow roses in the middle, signifying Meghan and Prince Harry's 2 children.

Thomas says he specifically wanted to incorporate his grandchildren, Archie and Lilibet, in Meghan's birthday flower arrangement ... telling us he wants to be a part of their lives because it seems to him the kids don't have enough family around them in Montecito.

As you know ... Meghan and her father have a testy relationship, and Thomas doesn't get along with Harry either.

Meghan and Harry also have a huge rift with the Royal family, and as we reported, the royals tweeted her happy birthday from their official accounts in what came off like calculated moves meant to keep up appearances.

Thomas says he didn't hear a peep from Meghan after he sent the gift, but he says that's fine and he's just hoping she likes the flowers.