Ephraim and Manasseh and Israel

Genesis 48:8-11 - When Israel saw the sons of Joseph, he asked, "Who are these?"

"They are the sons God has given me here," Joseph said to his father.
Then Israel said, "Bring them to me so I may bless them."

Now Israel's eyes were failing because of old age, and he could hardly see. So Joseph brought his sons close to him, and his father kissed them and embraced them.

Israel said to Joseph, "I never expected to see your face again, and now God has allowed me to see your children too."

Israel had been in Egypt for about 17 years, yet it sounds like this is the first time he met Joseph's sons, Ephraim and Manasseh. If so, I wonder why Joseph hadn't introduced them to their grandfather before now. The boys were roughly 20 years old. It's not like they were toddlers who might have been too much for Israel to handle.