11:48 AM PT -- Matt Barnes has weighed in on the engagement ... saying he's happy for EVERYONE involved!

"I have two beautiful boys from my ex we are both focussing on co-parenting & providing the best atmosphere & childhood for them," Barnes said ... "They love him, so I love it."

"Despite not seeing eye to eye initially w Derek he & I are on the same page & communicate weekly about Isaiah and Carter."

"With that being said congrats on the engagement!"

Good news for Derek Fisher ... the ex-NBA star popped the question to his girlfriend, Gloria Govan -- AND SHE SAID, "YES!"

We've learned ... 43-year-old Fisher got down on one knee during a small shindig at their Los Angeles-area home on April 7, surrounded by their kids and Gloria's nephew.

Derek had some of Gloria's friends take her out during the day so he could decorate the house while she was gone ... candles, flower petals ... it was romantic!

And yeah ... the ring's pretty big. We got a photo and you can see the diamond is the size of her knuckle!

Derek and Gloria have been dating since 2015. Both were previously married but have since divorced their significant others.

Of course, Gloria was married to Matt Barnes -- which caused some legendary drama between Derek and his ex-Lakers teammate. But Barnes recently said the beef is over and the two are now cool.

No word on when the two plan on officially tying the knot -- it's still early though.