Mystery Cactus Flower Buds

I have no idea what type of cactus this is. I had to remove a large one (see my 365th blip and my 730th blip) a year ago or so because it froze over the winter.  Brad felt bad for me and planted two little round ones from his garden.

They have now grown large enough - about 8 inches tall - to bud.  I expect at least one will bloom tomorrow.  It looks like the flowers may be pink, but we shall see.  They are huge buds.