Where are you? In many parts of the US lemons are typically produced from rooted cuttings and there is no bud union. Pictures of leaves and fruits would help. Also maybe something about the variety, rootstock if any, age of the tree.

I live in San Mateo. Don’t know the age I’ll have to ask them if the tree was there before them. Next visit will be next Tuesday. That’s when I’ll take a photo of the leaves and fruit.

Do most people not want 'large lemons'? Are you saying the limb with 'large lemons' is the rootstock that was left to grow? If so, I would just cut it off as close to the other trunk as you can. If this trunk was from rootstock, then the graft union is still above ground.

Do they recommend painting the cut branch stump in CA? I'm no tree expert.

Can we see a pic of the leaves and fruit of the branch in question?

I’ll take pictures next Tuesday. I do weekly maintenance at the clients house.

Here are some pictures of the leaves and fruit. The first two photos are of the normal side. The other photos are of the are of the suspected root stock branch.

The last photos are not a lemon; looks like a pomelo.... best guess, Cuban Shaddock. Cut off the limb of the "large lemons" where it comes off the trunk

I agree with John, it sure does look like Cuban S. The good news is that now you now know exactly what rootstock the lemon is on.

Thank everyone. I’ll let my client know what is happening and see if she is ok with me cutting that limb. She should be since she has told me before that she trust me with my decisions.